A massive galaxy with almost no dark matter

According to our prevailing cosmological models, Black 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 gauge its influence by observing dark matter halo, gravitational lenses, and the effect of general relativity on large-scale cosmic structures. And with the help of next-generation missions like ESA’s Euclid and NASA Nancy GraceRoman space telescopes, dark matter may no longer be a mystery!

And then something like this happens: a massive galaxy that appears to have little or no dark matter! This is precisely what a team of astronomers led by members of the Instituto Astrofisica de Canarias (IAC) noticed when observing NGC 1277. This lenticular galaxy, located 240 million light-years away in the constellation Perseus, is several times more massive than the Milky Way. It is the first time that a massive galaxy has been discovered that does not show signs of dark matter, which is a serious challenge for our current cosmological models.

The research was conducted by Sebastien Comeronan extragalactic astronomer at the Universidad de La Laguna (ULL), the IAC, and the head of the Archeology of Thick Discs (ArcThick). He was joined by researchers from the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), the Consejo Nacional de Ciencia y Tecnología, the National Academy of Sciences of Ukraine, the Instituto de Física de Partículas y del Cosmos (IPARCOS), the Max Planck Institute for Astronomy (MPA) and several universities. The article describing their findings recently appeared in the journal Astronomy & Astrophysics.

Hubble Space Telescope image of the Perseus cluster galactic cluster of which NGC 1277 is a member. It’s the bright galaxy just to the left of the center of the image. Credit: ESA/Hubble

According to the Standard Model of Cosmology – alias. THE Cold Dark Matter Lambda (?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 hydrogen gas into swirling disks. This gas was pulled 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 manifested in 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 distribution of the star. From this they deduced that the DM could not represent more than 5% of the galaxy’s mass within the observed radius – although their observations indicated that there might be no DM at all. As Comerón explained in a recent IAC press release:

“This result does not fit currently accepted cosmological models, which include dark matter. The importance of relict galaxies in helping us understand how the first galaxies formed was why we decided to observe NGC 1277 with an integral field spectrograph. From the spectra, we made kinematic maps that allowed us to determine the mass distribution 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 neighboring galaxies. These galaxies are thought to be the remnants of giant galaxies that formed shortly after the Big Bang. However, the ?CDM model predicts that the DM should represent at least 10% of galaxies as massive as NGC 1277, with a maximum of 70% for this particular type. Said co-author Anna Ferré-Mateu, researcher at IAC and ULL, there are two possible explanations for this discrepancy:

“One is that gravitational interaction with the surrounding medium within the galaxy cluster in which this galaxy is located removed dark matter. The other is that dark matter was driven out of the system when the galaxy formed through the fusion of protogalactic fragments, giving 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 Neptune’s orbit around the Sun. Credit: D. Benningfield/K. Gebhardt/StarDate

However, neither of these explanations is entirely satisfactory as far as the team is concerned. In the near future, the team plans to further investigate the mystery by making observations with the WHT Enhanced Zone Speed ​​Explorer (WEAVE) 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 were to confirm that NGC 1277 has no DM, it could cast serious doubt on alternative theories – such as Modified Newtonian Dynamics (MOND). Said Trujilo:

“This discrepancy between the observations and what we expected is a puzzle, and perhaps even a challenge for the standard model. Although dark matter in a specific galaxy may be lost, a modified law of gravity must be universal, it cannot have exceptions, so a galaxy without dark matter is a refutation of such kind of dark matter alternatives.

These observations could also shed light on the particularly enormous size of the galaxy. A supermassive black hole (SMBH), or 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 ms sourcewhich was formed from collapse of DM Halos at the beginning of the universe. There is also the mystery of dark matter galaxieslike the curious case of FAST J0139+4328which are almost entirely composed of DM.

Next-gen missions like Euclid and the Nancy GraceRoman space telescopes will also bring new insights by examining 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 settle the ongoing debate by revealing either that a mysterious invisible mass exists, or that our understanding of gravity (as described by general relativity) needs to be revised.

Further reading: IAC, Astronomy & Astrophysics

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