The Weizmann Experience: discussions on the future of cosmology

Together with Francoise Combes, who was recently appointed as a professor in the most prestigeous institution in France, Le College de France, and Benoit Famaey, who is an expert on Milgromian dynamics and its deeper foundations (e.g. Famaey & McGaugh 2012), we were invited by Mordehai (Moti) Milgrom to spend a whole week at the Department of Particle Physics and Astrophysics in the Weizmann Institute in Rehovot, Israel. A link to the video (dubbed in English) of the inaugural lecture given by Francoise Combes for her new chair and the introduction by Serge Haroche (Nobel Prize 2012 in physics) is available here (alternatives to the dark matter approach are explicitly mentioned by both).

I met Benoit at Frankfurt airport in the very early morning (he was heading in some random direction) since we had booked the same Lufthansa flight to Tel Aviv. We arrived on Sunday, March 6th, and met Moti at his office in the late afternoon.

In the entrance hall of the department. From left to right: Einstein's field equation without Lambda, Francoise Combes, Mordehai Milgrom, Pavel Kroupa and Benoit Famaey.
In the entrance hall of the Department. From left to right: Einstein’s field equation without Lambda, Francoise Combes, Mordehai Milgrom, Pavel Kroupa and Benoit Famaey.

Coming to know the place and first discussions

I am very impressed by the size and beautiful campus of the whole Weizmann Institut, and how pleasant the entire ambiente is.

Chairs and a pond infront of th Department.
Chairs and a pond infront of the Department.

The people are very friendly and helpful. And interested. I was staying at the spacious and luxurious San Martin Faculty Clubhouse. At night the various buildings and park areas in the Weizmann Institute are illuminated beautifully, with warm lights setting accents and emphasizing a welcoming atmosphere.

The highly-ranked  Weizmann Institute consists of many departments of various natural sciences and seems to be perfectly created for academic pursuit, including leisure areas. Its success in the pursuit of basic research in the natural and exact sciences and in acquiring funding is evident through the architecture, spaciousness, and general design.

There was no planned agenda for us, apart that Benoit was to give a talk on Wednesday, 9th of March, at 11:15, and for Francoise Combes to give a departmental colloquium on Thursday, 10th of March at 11:15. In between these talks we could do either nothing and hang about enjoying the sunshine and exquisite weather and pool, or engage in intense discussions. Perhaps due to the ambiente and of course our comparable research interests, we largely chose the latter.

On Monday, 7th of March, we had a very relaxed day, meeting with Moti at the Department in the late morning and spending our time debating. Typical discussion points (largely between Francoise, Benoit and myself) throughout the visit were the local major underdensity and its possible implications on the value of the cosmological Lambda, the underlying theory of MOND and whether it is due to a “dark” fluid which behaves like dark matter on large scales (e.g. Luc Blanchet’s dipoles and Justin Khoury’s condensate)

Given that Lambda was missing in the equation displayed in the entrance hall of the Department (see first photo above), we began to discuss it. And this is where the “local” underdensity now plays a possibly important role, see this figure from Kroupa (2015),

The underdensity is significant, according to the shown data, and may challenge any cosmological model. From Kroupa (2015).

 

and in contrast the very recent work by Whitbourn & Shanks where the authors explicitly state agreement with the previous survey by Kennen et al. (2014). The independent finding by Karachentsev (2012) on the local 50 Mpc scale appears to naturally continue the trend evident from the Kennan et al. data (see the figure on the left), IF one assumes the same baryonic to dark-matter ratio as at larger distances. The actually measured stellar density remains similar to the Keenan et al. value at small distance. So the baryonic density (assuming the gas to star ratio and the contribution by dwarf galaxies to remain unchanged out to distances of 800 Mpc [redshift of 0.2]) then within 300 Mpc there is at least a decrease in the baryonic density by factor of two. Conversely, taking Karachentsev’s measurement, we would see a disappearance of dark matter nearby to us since the stellar density remains similar to the Kennen measurement within 150 Mpc while the dark matter density decreases further. So the measurements appear to imply the following picture: within 400 Mpc the luminous (and thus baryonic) matter density decreases significantly by a factor of two. At the same time, the ratio of dark matter to baryonic matter decreases even more. Both findings violate the cosmological principle.

The work by David Wiltshire (his lecture notes) and Thomas Buchert already indicates that inhomogeneities could possibly make the Universe appear to an observer situated within such an underdensity as if it’s expansion is accelerating, although in truth it is not. That is, the inhomogeneities appear to be of the correct magnitude to eliminate the need for Lambda, Lambda (dark energy) merely being an apparent effect mis-interpreted by the supernova type 1a data. The reason lies in that a distant object’s observed redshift depends in reality on the exact paths the photons travel in a universe which consists of time-changing voids and over-densities, and this is a different redshift computed assuming a homogeneous and isotropic expanding Universe.

But we need more detailed calculations taking into account the constraints from the observed under-density shown in the figure to be assured that Lamba=0. It is certainly true that Lambda=0 may be more in line with theoretical ideas than the very small value deduced to explain an apparently accelerating Universe, because it is actually predicted, from quantum field theoretical calculations of the vacuum (for details see e.g. Padilla 2015), to have a value some 60 to 120 orders of magnitude larger. It should be emphasized, though, that “MOND likes Lambda“, in the words of Moti. The reason is that the Lambda derived from astronomical observations (e.g. from supernovae of type 1a observations) and Milgrom’s constant a_0 appear to be naturally related, and MOND may be derivable from vacuum processes (Milgrom 1999).

Within about 300 Mpc, where we can say that we have the best measurements, the Universe is nicely consistent with MOND. The mass-to-light ratios of galaxy groups are less than 10 (Milgrom 1998 and Milgrom 2002), i.e. there is only baryonic matter. The observationally inferred increased density of baryonic matter at distances larger than 300 Mpc would then perhaps be due to cosmological models being inappropriate, i.e. that the currently used red-shift–distance relation may be wrong.

We also debated galaxy evolution, the fraction of elliptical galaxies and the redshift dependence of this fraction. Notably, fig.7 in Conselice (2012)  shows that the observed fraction of massive galaxies does not evolve although the LCDM model predicts a strong evolution due to merging. This is consistent with the independent finding by Sachdeva & Saha (2016) that mergers are not a driving mechanism for galaxy evolution, and this is in turn consistent with the independent findings reached by Lena et al. (2014)  on the same issue.

We further talked about how LCDM is faring on large, intermediate and small  scales, how stellar populations change with physical conditions, the variation of the IMF, as well as political topics. The discussions were far from reaching consensus, we had different views and data sets we could quote on various problems, and time flew by such that we barely noticed.

However, Moti managed to drag us away from his Department, and showed us around the Weizmann institute. An particular station was the famous landmark tower which once housed the Koffler Accelerator and which now houses, in its “bubble”,

The tower which housed the Koffler Accelerator and which now houses a conference room (in its “bubble”) and the Martin S. Kraar Observatory.

a conference room and also the Martin S. Kraar observatory which is also used in international top-level research projects. The director of the observatory, Ilan Manulis, kindly explained to us in much detail its functionality and design for full remote-observations without human interference.

Viewing the lands from the top of the Koffler Accelerator Building. From left to right: Benoit Famaey, Francoise Combes and Mordehai Milgrom.
Part of the Weizmann Institute as viewed from the top of the Koffler Accelerator.
Part of the Weizmann Institute as viewed from the top of the Koffler Accelerator Building.
The "bubble" housing the conference room in the tower of the Koffler Accelerator.
The “bubble” housing the conference room in the tower of the Koffler Accelerator.
The Group at the Koffler Accelerator. From right to left: Benoit Famaey, Francoise Combes, Mordehai Milgrom and Pavel Kroupa.
The Group at the Koffler Accelerator. From right to left: Benoit Famaey, Francoise Combes, Mordehai Milgrom and Pavel Kroupa.

On this Monday Moti took us to lunch at the Lebanese restaurant Petra located in Nes-Ziona, a town 5 minutes drive from the Weizmann Institute. The Lebanese cuisine was fabulous, and I ate far too much.

 

A diversion to history

And, on Tuesday, 8th of March, Moti and his wife Ivon took us on a drive-around nearby Israel. This trip, involved about 4 hours of driving by Moti, and while driving we discussed, amongst other topics, the new study by Papastergis et al. (2016) in which they use 97 gas-dominated galaxies from the ALFALFA 21cm survey to construct their estimate of the baryonic Tully-Fisher relation showing excellent agreement with the expectations from Milgromian dynamics.

The drive was incredible, as we saw places with many thousands of years of history dating back to the Caananite peoples. It is this land which took the central role in the evolution of the Mediteranean-Sea-engulfing Roman Empire to a Christian empire. It contains the scars of the episodes of the invasion by a newer religion of christian lands, christian reconquest, and reconquest by the newer religion, till the foundation of Israel, issues which remain current to this day.

We visited Caesarea:

Caesarea, once a thriving port for many centuries, from where Paulus was imprissioned and sent to Rome for his hearing at the emperor's court, was wiped out in the 13th century.
Caesarea, once a thriving port for many centuries, from where Paulus was imprissioned and sent to Rome for his hearing at the emperor’s court, was wiped out in the 13th century.

The thriving thousand-yearold medieval city of Caesarea, named by King Herod after Octavian (i.e. Augustus Caesar) and which was once the main port in his kingdom, was finally obliterated from existence after a siege by a Mamluk army in the thirteenth century.

The ruins of Caesarea. King Herodot had his palace here.
The ruins of Caesarea. King Herod is supposed to have had his palace here.
The author amongst the ruins of Caesarea. "What was the fate of Caesarea's inhabitants when it fell to the Mamluks?"
The author amongst the ruins of Caesarea. “What was the fate of Caesarea’s inhabitants when it fell to the Mamluks?”
The Group in front of the Roman ampitheater in windy Caesarea, nearly but not quite ready.
The Group in front of the Roman ampitheater in windy Caesarea, nearly but not quite ready.
The Group in Caesarea, ready. From right to left: Mordehai Milgrom, Francoise Combes, Benoit Famaey, Pavel Kroupa.
The Group in Caesarea, ready. From right to left: Mordehai Milgrom, Francoise Combes, Benoit Famaey, Pavel Kroupa.

 

 

Acre, once a blossoming port and a gate-way to the holy lands for christian pilgrims.
Acre, once a blossoming port and a gate-way to the holy lands for christian pilgrims.

Acre: the chief port in Palestine during the crusader epoch still boasting major remains of the huge crusader’s fortress:

 

 

 

 

 

Acre: the remains of the Crusader port.
Acre: the remains of the Crusader port.
Acre was under the administration of the Knight's Hospitaller who helped arriving pilgrims and food was served in this Crusaders Refectory.
Acre was under the administration of the Knight’s Hospitaller who helped arriving pilgrims and food was served in this Crusaders Refectory.

After a wonderful dinner at the seashore between Tel Aviv and old Jaffa at the restaurant Manta Ray, where some action happened just before we arrived judging from the large number of police and other forces around, we visited very beautiful Old Jaffa:

Old Jaffa, which dates back to a history of 4000 years and where alrady the Egyptian empire stationed a garrison.
Old Jaffa, which dates back to a history of 4000 years and where alrady the Egyptian empire stationed a garrison.
Old Jaffa.
Old Jaffa.

The restoration of the archeological sites of Caesarea, Acre and of Old Jaffa brings to mind how incredibly rich and beautiful the thousand year old places are along the Mediterranean coast throughout the middle East and northern Africa, if upheld with the corresponding desire to show this history.

 

Back to science

On Wednesday, 9th of March, we spend the whole day in discussions with staff of the Institute. It began with Benoit Famaey’s presentation on the latest numerical results of modelling the Sagittarius satellite galaxy and its stream in Milgromian dynamics by Strasbourg-PhD student Guillaume Thomas. Natural solutions appear to emerge and this will, once published, clearly add spice to the discussions, given that the only solutions available in LCDM by Law & Majewski (2010) are unnatural in that the dark matter halo of the Milky Way needs to be oblate at right angle to the Milky Way, a solution which poses severe dynamical instabilities for the Milky Way disk. Notably, this polar oblate dark matter halo of the Milky Way alignes with the vast-polar structure (the VPOS) of all satellite galaxies, young halo globular clusters and stellar and gas streams.

In these discussions with the staff members during the aftenoon, we dealt with supernova rates and explosions and types in different galaxies, the relevance to the variation of the IMF in various environments (e.g. metal-poor dwarf galaxies vs metal-rich massive galaxies and the dependency of the IMF on density and metallicity), and cosmological problems such as the local massive under-density mentioned above.

An important point I tried to emphasize repeatedly is that if Milgromian dynamics is the correct description of galactic dynamics, then we must keep an open mind concerning the possibility that all of cosmological theory may have to be rewritten and the large-redshift data may need to be reinterpreted in terms of different redshift–distance and redshift–age relations.

In the evening of Wednesday I tried out the swimming pool on campus, and their sauna as well. I had access to this swimming pool by staying in The San Martin Faculty Clubhouse and the Hermann Mayer Campus Guesthouse – Maison de France. I must admit, that the day was near to being perfect with the sunshine and a closing dinner with Francoise and Benoit again in our meanwhile standard kosher restaurant (Cafe Mada) nearby the San Martin guest house.

On Thursday, 10th of March, Francoise Combes gave her interdepartmental presentation on “The Molecular Universe” which was well visited, and afterwards we went together with some staff of the Weizmann Institute for lunch at Cafe Mada, where a lively and very entertaining discussion ensued on religeos questions. In the late afternoon we joined the Whisky lounge, in which anyone traveling back to Rehovot from abroad can bring a duty-free bottle of Whisky to and donate it to this lounge.

The Local Group of galaxies is highly symmetrical, with all non-satellite dwarf galaxies lying in two planes symmetrically and equidistantly situated around the axis joining the Milky Way and Andromeda. From Pawlowski et al. (2013).
The Local Group of galaxies is highly symmetrical, with all non-satellite dwarf galaxies lying in two planes symmetrically and equidistantly situated around the axis joining the Milky Way and Andromeda. From Pawlowski et al. (2013).

Young researchers meet every Thursday (remember, this is in Israel the end of the week) to sip Whisky and thereby to elaborate on various problems, such as in our case on the local underdensity, or how the two critical constraints we have from the highly organized structure of the Local Group of galaxies and the CMB together constrain the cosmological model.

An interesting statement made was that while one needs about ten LCDM Universes to get one Bullet cluster (Kraljic & Sarkar 2015), an infinite number of LCDM Universes will not give a single Local Group with its symmetries.

At least these are some of the questions we discussed while there on this Thursday. We were also impressed by all the connections of this Department with Princeton, Caltech and Harvard.

Friday and Saturday

Shops begin to close down and it becomes a challenge to find food and Francoise left for France. In the morning I went for a swim and sauna, and for luch Benoit and myself had to go out of the Weizmann Institute (exit Main Gate and turn left) to find a sandwich place.

The Basha Bar in Tel Aviv.

 

After some work and then in the evening and at about 18:00 we decided to take a taxi to Tel Aviv. We arrived at the Basha Bar by about 18:30 and stayed for three hours (see photo).

 

The Basha Bar, enjoying a three-hour shisha smoke and many Tuborg beers.
The Basha Bar, enjoying a three-hour shisha smoke and many Tuborg beers.

On Saturday, the kosher breakfast in the guest house was as excellent as ever, but it was interesting for me to note that neither the toaster nor the coffee machine were to be used, while the water boiler was on so we could still have hot Turkish coffee (which we also drink in Bohemia, by the way, so not much new for me here). Nearly everything is closed. Benoit and myself met for lunch and walked outside the Main Gate turning right, over the bridge to reach the Science Park finding bistro Cezar for lunch.

In the evening Moti picked us up for a dinner at his home with Ivon, where we had a long discussion also on the dynamic situation in Germany, Europe and the future.

At the home of Moti in Rehovot.
At the home of Moti in Rehovot. From right to left: Moti, Benoit and the author.

 

Final comments

Benoit and myself stayed on until Monday, joining the astrophysics journal club which serves lunch at the Department on Sunday. I spent most of the afternoon discussing with Boaz Katz how star clusters may be relevant for type 1a supernovae. In the evening of Monday Benoit and I went again to Cafe Mada for a final dinner and drinks. On Monday, 14.03., we flew out around 16:00, taking a taxi to the Tel Aviv airport at 13:00 from the Department. We shared the same flight back. Again the 4+ hour long Lufthansa stretch without personal-screen-based entertainment system! But, this gave Benoit and myself a chance to further discuss at length the above mentioned Khoury condensate and the Blanchet dipoles as models for galaxy-scale MOND and cosmology-scale dark-matter-like behaviour. But I note that these are not dark matter models. During pauses my thinking was that as the coastal line of Tel Aviv receded in the setting Sun we left a small fraction of the Levant and northernmost Africa, all once pat of the Roman Empire, at a level of civilisation mirrored by the clear, brllliantly lit vast and dynamic power- and resource-hungry central-European night with full autobahns, radiant towns and illuminated football fields in nearly every village. In Frankfurt our ways parted after a last small dinner in the train station, Benoit taking a bus to Strasbourg at about 21:30, and me starting my odessey to Bonn at the same time using the available train connections (German trains all too often run late, these days).

The visit was most memorable for all of us, and Benoit and myself agree that we would like to return. We did not reach any conclusions but we came to know many new people and perhaps helped to underscore the very seriousness of alternative concepts to dark matter and the many failures of the LCDM model.

In closing it is probably fair to say that Milgrom contributed the greatest advance on gravitational physics since Newton and Einstein.

 

In The Dark Matter Crisis by Pavel Kroupa and Marcel Pawlowski. A listing of contents of all contributions is available here.

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First Workshop on Progress in Modelling Galaxy Formation and Evolution in Milgromian dynamics — first results achieved with the Phantom of Ramses (PoR) code

[Note: This web-page is being updated continuously:
current status: 26.09.15]

LOCATION and TIME:
Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS UMR 7550, Sept. 21st - 25th 2015

Below are provided
1.BACKGROUND/MOTIVATION
2.HOW TO REGISTER
3.PARTICIPANTS
4.HOTELS
5.PROGRAMME
6.PHANTOM WIKI
ORGANISERS: Benoit Famaey (Strasbourg) and Pavel Kroupa (Bonn)

1.BACKGROUND / MOTIVATION: Galaxy-scale data seem to be in accordance with the hypothesis that the extrapolation of Newtonian gravitation by orders of magnitude below the Solar system space-time curvature breaks down completely, and that collisionless astronomical systems behave according to space-time scale-invariant dynamics, as postulated by Mordehai Milgrom (2015). The classical theories of dynamics and gravitation underlying this symmetry, often referred to as MOND  theories, show a richer dynamical behaviour with new phenomena which appear non-intuitive to a Newtonian mind. Very successful analytical results have been obtained in this dynamics framework, such as accounting for the hitherto not understood properties of polar-ring galaxies (Lueghausen et al. 2013), accounting for the Bullet cluster (Angus, Fmaey & Zhao 2006Angus & McGaugh 2008) and the properties of disk galaxies (MOND reviews by Scarpa 2006; Famaey & McGaugh 2012;Trippe 2014) and elliptical galaxies (Sanders 2000; Milgrom & Sanders 2003; Scarpa 2006).

But little understanding of the dynamical behaviour of live Milgromian systems has been gathered. Live calculations, i.e. simulations of galaxies, are required in order to test, to possibly refine or to falsify this approach. The implications for fundamental physics are major in any case!

A series of Milgromian-dynamics workshops is planned to begin remedying this situation.

With this first “Phantom of Ramses” (PoR) meeting, the aim is to bring together the pioneers who have been daring footsteps into applying Milgromian dynamics to simulate live galaxies. First simulations of galaxies within MOND have been achieved with the first Milgromian Nbody code without gas (Brada & Milgrom 1999). Tiret & Combes (2007) re-visited this problem with their own code. The PhD thesis of Tiret is available here (in French). For spheroidal geometries MOND simulations have become possible with the NMODY code by Nipoti, Londrillo & Ciotti (2007), see e.g. the application of this code to the phase-transition of spheroidal systems on radial orbits (Wu & Kroupa 2013). A MOND code has also been developed for studies of cosmological structure formation by Ilinares, Knebe & Zhao (2008). While being highly successful in their ability to represent observed galaxies, all of these attempts have died-off due to a lack of long-term sustainability.

Now much more involved and more numerous studies has become possible with the first publicly available Milgromian dynamics computer code including star formation, i.e. baryonic physics (Lueghausen, Famaey & Kroupa 2015) with which even full-scale simulations of cosmological structure formation have become achievable, PoR being an official patch to Teyssier’s RAMSES code. A similar computer code (RAyMOND) has been developed independently by a Chilean research group (Candlish, Smith & Fellhauer 2015).

Because non-linear Milgromian dynamics is largely non-intuitive for researchers trained to think within the framework of linear Newtonian gravitation, this group of pioneers needs to find the chance to discuss, in as great depth as is required, the issues arising with initialising, setting-up and evolving Milgromian galaxies in virial equilibrium, including gas dynamics and star formation. The first scientific results which have already been achieved with the PoR code will be discussed at this occasion, but research related to Milgromian dynamics (e.g. by adoption of zeroth-order approximations by adding dark matter particles to Newtonan systems) will also be discussed.

The meeting will take place at the Observatoire astronomique de Strasbourg. We are planning a whole week for this event, whereby there will be one to two (at most three)  presentations per day interrupted with long discussion breaks to dwell upon problems that have been encountered and that may need solutions. Also, the breaks are intended to allow new persons to learn using PoR. The meeting will take place in the *MEETING ROOM* (with a capacity of about 20) at the Observatoire, and the presentations can be of any duration, but must have a break after the first 45 minutes if longer. After the last presentation each day discussions may continue at will, and Strasbourg offers many excellent culinary opportunities for the evening entertainments.

2.HOW TO REGISTER / IF INTERESTED:
Please register by sending an e-mail to Benoit Famaey <benoit.famaey_at_astro.unistra.fr> and to Pavel Kroupa <pavel_at_astro.uni-bonn.de>.

Note that this meeting does not have invited talks. The attendance is limited to 20.
3.PARTICIPANTS (preliminary):

Garry Angus (Brussel, Belgium)
Indranil Banik (St. Andrews, UK)
Christian Boily (Strasbourg, France)
Joerg Dabringhausen (remotely from Concepcion, Chile)
Benoit Famaey (Strasbourg, France) [SOC]
Martin Feix (Paris, France)
Hector Flores (Paris, France)
Alistair Hodson (St. Andrews, UK)
Rodrigo Ibata (Strasbourg, France)
Tereza Jerabkova (Praha, Czech Rep.)
Pavel Kroupa (Bonn, Germany) [SOC]
Fabian Lüghausen (Bonn, em.; tbc)
Marcel Pawlowski (Cleveland, USA)
Florent Renaud (Surrey, UK)
Jean-Babtiste Salomon (Strasbourg, France)
Ingo Thies (Bonn, Germany)
Guillaume Thomas (Strasbourg, France)
Yanbin Yang (Pairs, France)
HongSheng Zhao (St. Andrews, UK)

Conference Photo (24.09.2015):

PoR_group
Left to right:  Yanbin Yang, Indranil Banik, Ingo Thies, Guillaume Thomas, Garry Angus, Jean-Babtiste Salomon, Tereza Jerabkova, HongSheng Zhao, Rodrigo Ibata, Marcel Pawlowski, Hector Flores, Alistair Hodson, Florent Renaud, Benoit Famaey, Fabian Lueghausen, Pavel Kroupa
4.HOTELS:

Hotel Esplanade
ETC Hotel
Hotel Roses
Hotel21
Au Cerf d’Or
des Princes
5.PROGRAME:
The programme, abstracts and list of participants are available here as a pdf file:
PoR_Programme.pdf


PROGRAM (with downloadable presentations):  

First Workshop on Progress in Modelling Galaxy Formation and Evolution in Milgromian dynamics —
first results achieved with the Phantom of Ramses (PoR) code.
At the Observatoire astronomique de Strasbourg, 21.09.-25.09.2015.

PoR-code talks are scheduled for the afternoons allowing for discussion and learning time.  A few scientific talks relevant to the mass-deficit problem are scheduled for the mornings.


******* Sunday, 20th September

evening, approximately 18:00-
Meet for drink and food at Au Brasseur
ACCUEIL
******* Monday, 21st September 10:00 MORNING COFFEE 10:30 Welcome/Introduction/First presentation and discussion: Setting the scene: 1. Kroupa_PoR.pdf: Why is the dark-matter approach ill-fated? (Pavel Kroupa) 2. Famaey.pdf: The basics of Milgromian dynamics/MOND (Benoit Famaey) LUNCH (12:15-14:45) 15:00-16:15 1. Lueghausen_PoR.pdf: The PoR code (Fabian Lueghausen) 2. Thies_PoR.pdf: Setting up a stable disc galaxy in PoR (Ingo Thies) 16:30 AFTERNOON TEA 17:00-18:00  Open Discussion ******* Tuesday, 22nd September 10:00 MORNING COFFEE 10:45-11:15 (30 minutes) Angus_PoR.pdf: The DiskMass Survey’s implications for MOND, CDM and itself  (Garry Angus) LUNCH (12:15-14:45)   14:45-15:15 (30 minutes) Banik.pdf: The External Field Effect In QUMOND: Application To Tidal Streams (Indranil Banik) 16:10 AFTERNOON TEA 16:30 Thomas_PoR.pdf: Simulating Tidal Streams with PoR (Guillaume Thomas) PoR Movie (dSph Sgr, slide 19 in presentation): YouTubelink 17:00-18:00  Open Discussion - decision to set up PhantomWIKI ******* Wednesday, 23rd September 10:00 MORNING COFFEE 10:45-11:15 Yang_PoR.pdf: (30 minutes) Reproducing properties of MW dSphs as descendants of DM-free TDGs (Yanbin Yang) MEETING PHOTO  (12:15) LUNCH (12:20-14:45) 14:15-14:45 Angus2_PoR.pdf: The sub-subhalo connection to M31’s plane of satellites (Garry Angus) 14:45-15:15 Pawlowski_PoR.pdf: (30 minutes) Small-scale problems of cosmology and how modified dynamics might address them (Marcel Pawlowski) 16:00 AFTERNOON TEA 16:30 Renaud_PoR.pdf: Gravitation-triggered star formation in interacting galaxies (Florent Renaud) 17:30-18:00  Open Discussion 18:30--  Workshop dinner at Au Brasseur
ACCUEIL
******* Thursday, 24th September 10:30 MORNING COFFEE 10:45-11:15 Hodson_PoR.pdf: (30 minutes)  EMOND (Extended MOND) and effective galaxy cluster masses (Alistair Hodson) 11:30-12:00 Preliminary results on QMOND forces between point masses (HongSheng Zhao) LUNCH (12:15-14:45) 14:45-15:15  Salomon_PoR.pdf: The tangential motion of the Andromeda System (Jean-Babtiste Salomon) 15:15-15:45 Dabringhausen_PoR.pdf: Early-type galaxies in Milgromian dynamics (Joerg Dabringhausen, remotely from Concepcion, Chile) 16:15 AFTERNOON TEA 16:45-17:15 Banik2_PoR.pdf: Evidence for Dynamical Heating in The Local Group (Indranil Banik) 17:15-18:00  Open Discussion ******* Friday, 25th September 10:00 MORNING COFFEE 10:30-12:00 Kroupa_IMF_Strasbrourg.pdf Main Seminar of the Observatory: Is the stellar IMF a probability distribution function, or is star formation highly regulated? (Pavel Kroupa) LUNCH (12:15-14:45) 15:00 Final discussion and FAREWELL
6.PHANTOM WIKI

PhantomWIKI
This wiki is dedicated to supporting the research making use of the “Phantom of RAMSES” (PoR) patch.

This blog moves to SciLogs.com

Pavel and I have been too busy to blog for a while (my excuse being that I am in the final stages of my PhD studies). This is also why we did not announce this sooner: Our blog has moved from SciLogs.eu to SciLogs.com. The new site provides an improved blogging system and maybe more international visibility, as well as a pleasant neighborhood of science bloggers. The new URL for "The Dark Matter Crisis" is http://www.scilogs.com/the-dark-matter-crisis/. All future articles will be published there, but the old ones will remain accessible here on SciLogs.eu.

The first article on the ‘new’ blog deals with last week’s Nature article by Rodrigo Ibata and collaborators: "A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy". While the media currently focusses on the 15-year old co-author of the Nature study, the scientific implications of the study are no less spectacular. The co-rotating plane of satellite galaxies around Andromeda resembles the VPOS around the Milky Way and therefore similar formation scenarios are plausible, which we discuss in our article "Andromeda’s satellites behave as expected … if they are tidal dwarf galaxies".

A filament of dark matter between two clusters of galaxies: dark matter detected

We briefly comment on the paper by Dietrich, Werner, Clowe et al. on “A filament of dark matter between two clusters of galaxies ” which is now in press with Nature.

The media have it that this may be a direct detection of dark matter.  The abstract of this paper reads

“It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this “cosmic web” has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.”

The first sentence of the abstract is undoubtedly correct, but the following sentence here is absolutely true as well:

“It is a firm prediction of any realistic cosmological model that galaxy clusters live at the intersection of large-scale structure filaments.”

Indeed, in any realistic theory of gravity, matter, which has a significant random velocity field, will collapse to filamentary structures. This is amply observed in simulations of molecular clouds without dark matter and is now also beautifully seen in observations of real molecular clouds with the Hershel telescope (e.g. Andre et al. 2010). Filamentary structure is thus nothing special to the  concordance Cold Dark Matter (CDM) cosmological model, and so the abstract can be seen as being somewhat misleading.

Further,  the authors of this paper have only studied the lensing signal using Einstein’s General Relativity. It is true that using Einstein’s General Relativity the signal can only be interpeted with the help of postulating the presence of additional, unseen matter.

But, in a different but nevertheless realistic theory of gravity, the lensing signal may well be explainable without dark matter (e.g. Zhao et al. 2006). It is even possible that in a better theory of gravity, if there is a matter concentration at point A and one at point B then there might be a lensing signal not related to any local matter density at point C in between A and B. Wrongly interpeting such a lensing signal with General Relativity would then lead to the false result that there is unseen matter at C. For instance, in this paper Mordehai Milgrom and Robert Sanders explain how a dark matter effect appears where there is no dark matter at all. The gravitational lensing by filaments in the framework of modified gravity has also been investigated by Feix et al. (2008).

So, the above Nature paper is misleading on this account as well, because “the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system” relies on assuming effective gravity to be described by Einstein’s General Relativity on all scales.

That this cannot be the case has already been shown many times (e.g. “What are the three best reasons for the failure of the LCDM model? Incompatibility with observations” and “Question CII: MOND works far too well!“).  And, an invited review on these problems and matters is available as a freely-downloadable open access CSIRO-publishing paper “The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology”.

So, while the observations and the results presented in the Nature paper are a major and beautiful feat deserving much attention, a more balanced discussion of the results would have been more appropriate.

By Pavel Kroupa and Marcel Pawlowski  (05.07.2012): “A filament of dark matter between two clusters of galaxies” on SciLogs. See the overview of topics in  The Dark Matter Crisis.

13th Marcel Grossmann Meeting

We are now on our way to the 13th Marcel Grossmann Meeting in Stockholm. The meeting of physicists and astronomers covers General Relativity, Gravity and relativistic field theories and is held every three years (since 1975) in different cities. It is named after Marcel Grossmann, who was a Swiss mathematician and a collaborator of Einstein in his work on general relativity.

Following his recent review paper “The dark matter crisis: falsification of the current standard model of cosmology”, Pavel has been invited by Davit Merrit to give a talk in the parallel session “EG4: Self-Gravitating System”.

The session will take place tomorrow afternoon (Tuesday, 3rd of July) at the AlbaNova University Center, in room FA32. We will present our work on the dwarf and satellite galaxies in the second half of the session, after the coffee break at 16:30. At first, Marcel will give a talk on the Vast Polar Structure (VPOS) and why filamentary accretion can not account for it. This is followed by Pavel (at 16:45) presenting his falsification of the standard model of cosmology. The third talk in this row (17:05) then is by Mordehai Milgrom, who first proposed Modified Newtonian Dynamics (MOND) as an alternative to dark matter. He will present “MOND laws of galactic dynamics”.

The session will continue until 18:50 with more talks on dark matter, its haloes and galaxy formation. We are looking forward to an interesting meeting with lots of discussions. If we find the time, we might even report on some aspects of the meeting here in the blog.

By Pavel Kroupa and Marcel Pawlowski  (02.07.2012): “13th Marcel Grossmann Meeting” on SciLogs. See the overview of topics in The Dark Matter Crisis.

Discussing Gravity with Erik Verlinde

We have just returned from a talk by the Bethe colloquium. Erik Verlinde from the university of Amsterdam spoke about “Dark Matter, Dark Energy and the Emergence of Gravity ”.

Verlinde is a dutch theoretical physicist working on string theory and gravity. He became very famous for his theory of entropic gravity and was awarded the Spinoza Prize for his work.

In his talk, he showed that his approach can not only reproduce the MONDian behavior of the different kinds of galaxies. He even gave an explanation on why the centers of galaxy clusters deviate from the baryonic Tully-Fisher relation by a factor of four. The reason, he says, lies in the distribution of matter. Very roughly, galaxies can be approximated by a point mass if we look at their outskirts only. In galaxy clusters, however, the matter is more evenly distributed. Assuming a spatially constant matter density, he can even motivate the amount of the deviation

All in all, his results look very promising. After the talk, Pavel and I discussed with him for about an hour, explaining some of the failures of the LCDM model, but mostly asking about details and implications of his approach. He explained that his intention is to understand gravity by starting from scratch. So not only change and modify the formula used so far, but basing our understanding of gravity on a more fundamental basis. To do so, he looks at the observational evidence unbiased. We agreed that this is not always easy because especially cosmological results are usually analyzed and expressed in a model-dependent form. He does not aim at reproducing MOND, which even its adherents usually describe rather as a phenomenological effect than a new fundamental law. But his model naturally contains MONDian behavior, it seems to explain/give a reason for MOND’s free parameter (the acceleration a0) and he also showed that his approach can predict the ratio of baryonic to (phantom) dark matter correctly: 4% to 22.5%.

What he told was impressive and looks like it could be a major step forward in our understanding of gravity and the universe. Unfortunately, we have to wait some more until he will publish a paper on this topic. But there is good reason to look forward to it.

By Pavel Kroupa and Marcel Pawlowski  (28.06.2012): “Discussing Gravity with Erik Verlinde” on SciLogs. See the overview of topics in  The Dark Matter Crisis.

Does filamentary accretion of dark matter sub-halos naturally produce a VPOS-like structure?

In the previous post we discussed the VPOS, the vast polar structure of satellite objects around the Milky Way. One of the suggested origins within the cosmological cold dark matter paradigm is that the satellites have been preferentially accreted along large, cosmic filaments. These are long, thread-like structures which arise naturally during the formation of structure in the cosmos. The movie below shows how they come about:

 

One work suggesting that filamentary accretion can solve the VPOS-problem is Lovell et al. (2011). Its abstract claims that:

“All [six] haloes [of the Aquarius simulations] possess a population of subhaloes that rotates in the same direction as the main halo and three of them possess, in addition, a population that rotates in the opposite direction. These configurations arise from the filamentary accretion of subhaloes. Quasi-planar distributions of coherently rotating satellites, such as those inferred in the Milky Way and other galaxies, arise naturally in simulations of a ΛCDM universe.

Note the part we marked in bold face. This statement of theirs suggests that a structure like the VPOS is a natural outcome of cosmological simulations, which arises due to the filaments around a dark matter halo. That filaments can lead to anisotropies in the direction from which sub-halos are accreted onto larger halos is obvious, and it was a good idea that this might be a way to form anisotropic distributions of subhalos. However, there are several reasons to doubt this scenario.

First of all, the filaments are way too thick. For example, in Vera-Cirro et al (2011) it is shown that the filaments in the Aquarius simulations are very wide, of the order of 0.5 – 1 Mpc (see figure below). The VPOS has a thickness of only about 50 kpc. There is no way it can have been formed out of a much bigger filament. The filaments are in fact larger than the halo of the main galaxy (virial radius 200-250 kpc). Vera-Cirro et al (2011) write:

“[…] when the surrounding filament is sufficiently wide, i.e. of comparable or larger cross-section than the virial radius of the halo, the infalling particles will appear to be more isotropically distributed on the sky […]. We have argued  […] that [this] case is characteristic of the late stages of mass assembly in  10^12  Msun objects.”

This statement is contrary to the Lovell et al. (2011) one. In the simulations Vera-Cirro et al. (2011) discuss, the filaments are much wider than the central halo for most of the time of the simulation (from about 5 Gyr on). Thus, for about the past 9 Gyr, the accretion must have been more isotropically. Interestingly, the Vera-Cirro et al. (2011) work is based on the Aquarius simulations, the same set of cosmological simulations as the Lovell et al. (2011) paper. And it has been accepted for publication before the Lovell et al. (2011) paper.

Illustrating filament size from Vera-Cirro et al. 2011

Caption: Part of figure 4 of Vera-Ciro et al. (2011). It illustrates the size of a cosmic filament around a Milky Way like halo. The virial radius of the central halo is shown by the white ellipse. The thickness of the VPOS is less than one 10th of the white line at the bottom giving the scale of about 700 kpc.

In addition to this, the orientation of the preferred direction of orbits of subhalos is at odds with the expectations. Lovell et al. (2011) show that there is a slight over-abundance of subhalos orbiting in the same direction as the main halo (and in some cases also in the opposite direction). However, the galaxies forming in the main halos preferentially spin in the same direction as the main halo, so the sub-halo over abundance lies in the same plane as the galactic disc. In the case of the VPOS around the MW, the orientation is perpendicular.

Finally, Lovell et al. (2011) did not test the rather strongly worded statement of their abstract quantitatively. From their figures, it is already obvious that the before mentioned over-abundance of co-orbiting subhalos is small, only a factor of about 2 compared to the isotropic case in the bin closest to the main halo spin. The majority of subhalo orbital directions is distributed more evenly around the main halo.

Aquarius Orbital Poles

MW satellite orbital poles

Caption: The directions of angular momentum vectors, called orbital poles, of sub-halos coming from a cosmological cold-dark matter simulation (upper) and satellite galaxies of the Milky Way (lower). The question we addressed in our recent paper was: how likely is it that a distribution like the observed (lower) one can arise when drawing from the modeled (upper) one.

To allow a fair comparison, we have developed a method to test this claim. It is described in our recent paper “Can filamentary accretion explain the orbital poles of the Milky Way satellites?” (by Marcel S. Pawlowski, Pavel Kroupa, Garry Angus, Klaas S. de Boer, Benoit Famaey and Gerhard Hensler). In it, we determine how likely it is to find sets of angular momenta in model data (e.g. upper plot in the figure above) which are as concentrated and as close to a polar orientation as is observed for the MW satellite orbital poles (lower plot in the figure above). We have applied the method to both cosmological simulation data as well as models of galaxy collisions resulting in polar distributions of tidal debris.

The results are clear. They unambiguously disfavor the cold dark matter models.

Part of Fig. 3 from Pawlowski et al. 2012b

Caption: A part of Fig. 3 of our paper, illustrating the results of one of our criteria. The plot shows how likely it is that orbital poles derived from  models can be at least as concentrated as the observed value of 35.4 degree. The integral below the curves within the shaded region give the probability that randomly drawn orbital poles from the model are as concentrated as is observed. The two cosmological simulations (Aquarius D2 and Via Lactea 1, upper panels) show curves which are very similar to that for an isotropic distribution of satellite galaxies (thin line), it is unlikely that they fall into the shaded area. The lower panel shows the results for tidal debris of a galaxy collision, which is much more concentrated towards the left. In this latter case, it is most likely to draw orbital poles as concentrated as observed.

Using data from high-resolution cosmological simulations of halos that should host Milky-Way-like galaxies, we were able to show that the sub-halo orbits do not naturally produce the observed properties. In contrast, models in which the satellite galaxies are formed as tidal dwarfs from the debris of a galaxy-collision can easily reproduce the observed distribution of orbital poles. The claim that cosmological ΛCDM simulations naturally produce satellite distributions as inferred in the Milky Way has therefore been falsified. At the same time, this shows that the tidal scenario passes the test.

For more details, please read our paper (accepted by MNRAS). It is available as a preprint.

By Pavel Kroupa and Marcel Pawlowski  (15.05.2012): “Does filamentary accretion of dark matter sub-halos naturally produce a VPOS-like structure?” on SciLogs. See the overview of topics in  The Dark Matter Crisis.