A huge galaxy with almost no dark matter

According to our predominant cosmological models, dark matter accounts for about 85% of the mass of the Universe. While ongoing efforts to study this mysterious, invisible mass have yielded no direct evidence, astrophysicists have been able to measure its influence by observing dark matter halos, gravitational lensing, and the effect of general relativity on large-scale cosmic structures. And with the help of new generation missions such as those of ESA Euclid and NASA Nancy Grace Romana space telescopes, dark matter may not be a mystery for much longer!

And then something like this comes along: a huge galaxy that appears to have little or no dark matter! This is exactly what a team of astronomers led by members of the Instituto Astrofisica de Canarias (IAC) noticed while observing NGC 1277. This lenticular galaxy, located 240 million light-years away in the constellation Perseus, is many times more massive than the Milky Way. This is the first time a massive galaxy has been found that shows no signs of dark matter, which poses a serious challenge to our current cosmological models.

The research was led by Sbastien Comern, an extragalactic astronomer at the Universidad de La Laguna (ULL), the IAC and the leader of the Archology of Thick discs (ArcThick) collaboration. It was joined by researchers from the Instituto Nacional de Astrofsica, ptica y Electrnica (INAOE), the Consejo Nacional de Ciencia y Tecnologa, the National Academy of Sciences of Ukraine, the Instituto de Fsica de Partculas y del Cosmos (IPARCOS), the Max Planck Institute for Astronomy (MPA), and several universities. The paper describing their findings recently appeared in the journal Astronomy and astrophysics.

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Hubble Space Telescope image of the galactic group in the Perseus Cluster of which NGC 1277 is a part. It is the bright galaxy just to the left of center in the image. Credit: ESA/Hubble

According to the Standard Model of Cosmology – aka. the Lambda Cold Dark Matter (?CDM) model – Dark matter played an intrinsic role in the formation and evolution of the cosmos (and still does). In theory, this invisible mass existed shortly after the Big Bang and formed halos that attracted neutral gaseous hydrogen into swirling disks. This gas was drawn into increasingly dense clouds, triggering the formation of the first stars and galaxies. Today, the DM is a major component of all massive galaxies and is evident from their rotation curves, the lenses they create, and their interactions with surrounding stars and the intergalactic medium (IGM).

However, when the team measured the mass distribution of NGC 1277, they only observed the star’s distribution. From this, they deduced that DM could represent no more than 5% of the mass of the galaxy within the observed radius, although their observations indicated that there may not be DM at all. As Comern explained in a recent IAC press release:

“This result does not fit currently accepted cosmological models, which include dark matter. The importance of relic galaxies in helping us understand how the first galaxies formed was the reason we decided to observe NGC 1277 with an integral field spectrograph. From the spectra we obtained kinematic maps that allowed us to calculate the distribution of mass within the galaxy up to a radius of about 20,000 light years”.

In their paper, the team describes NGC 1277 as a prototype ‘relic galaxy’, a very rare class that does not interact with nearby galaxies. These galaxies are believed to be remnants of giant galaxies that formed shortly after the Big Bang. However, the ?CDM model predicts that the DM should account for at least 10% of massive galaxies like NGC 1277, with up to 70% for this particular type. There are two possible explanations for this discrepancy, said co-author Anna Ferr-Mateu, a researcher at the IAC and the ULL.:

One is that gravitational interaction with the surrounding medium within the galaxy cluster in which this galaxy is located has stripped away the dark matter. The other is that dark matter was expelled from the system when the galaxy formed from the fusion of protogalactic fragments, which gave rise to the relic galaxy.

This diagram shows how the diameter of the 17 billion solar mass black hole at the heart of the galaxy NGC 1277 compares to the orbit of Neptune around the Sun. Credit: D. Benningfield/K. Gebhardt/StarDate

However, none of these explanations are fully satisfactory as far as the team is concerned. In the near future, the team plans to investigate the mystery further by conducting observations with the WHT Enhanced Area Velocity Explorer (WEAVE) instrument on the William Herschel Telescope (WHT), located at the Roque de los Muchachos Observatory on the island of La Palma. If WEAVE’s velocity measurements confirm that NGC 1277 has no DM, they could cast serious doubt on alternative theories, such as Modified Newtonian Dynamics (MOND). Trujillo said:

“This discrepancy between the observations and what we would expect is a conundrum, and perhaps even a challenge to the standard model. Even if dark matter in a specific galaxy can be lost, a modified law of gravity must be universal, it cannot have exceptions, so a galaxy without dark matter is a refutation of this kind of alternatives to dark matter.”

These observations could also shed light on the galaxy’s massive supermassive black hole (SMBH), which is about 17 billion solar masses, or 4,250 times that of Sagittarius A* (the SMBH at the center of the Milky Way)! According to some astronomers, black holes could be the source of DM, which formed from the collapse of DM Halos during the early Universe. There is also the mystery of Dark Matter Galaxies, such as the curious case of FAST J0139+4328, which are almost entirely composed of DMs.

Next generation missions like Euclid and the Nancy Grace Romana space telescopes will also provide new insights into the expansion of the cosmos since the Big Bang. These observations aim to measure the influence of Dark Matter (and Dark Energy) on the largest of cosmic scales. The results of these and other studies will resolve the ongoing debate by revealing that a mysterious invisible mass exists or that our understanding of gravity (as described by General Relativity) needs to be revised.

Further reading: IAC extension, Astronomy and astrophysics

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