According to our common cosmological models, Dark Matter accounts for about 85% of the mass in the Universe.

Although ongoing efforts to study this mysterious, invisible mass have not provided direct evidence, astrophysicists have been able to quantify its influence by observing Dark Matter Halos, gravitational lenses and the effect of General Relativity on large-scale cosmic structures.

With the help of next-generation missions like ESA's Euclid and NASA's Nancy Grace Roman space telescopes, Dark Matter may not be a mystery for much longer!

And then something like this appears: A gigantic galaxy where there appears to be little or no Dark Matter at all! This is exactly what a team of astronomers led by members of the Instituto Astrofisica de Canarias (IAC) noticed while observing NGC 1277.

Located 240 million light-years away in the constellation Perseus, this lenticular galaxy is several times more massive than the Milky Way. This is the first time a large galaxy has been found that shows no signs of Dark Matter, a serious challenge to our current cosmological models.

The research was led by Sébastien Comerón, extragalactic astronomer at Universidad de La Laguna (ULL), IAC, and leader of the Archæology of Thick discs (ArcThick) collaboration.

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 many universities. The paper describing their findings was recently published in the journal Astronomy & Astrophysics.

According to the Standard Model of Cosmology - also known as the Lambda Cold Dark Matter (ΛCDM) model - Dark Matter played (and still plays) an intrinsic role in the formation and evolution of the cosmos.

Theoretically, this invisible mass came into existence shortly after the Big Bang, forming halos that pulled neutral hydrogen gas into rotating discs. This gas was drawn into denser and denser clouds, triggering the formation of the first stars and galaxies.

Today, DM are an important component of all massive galaxies and are recognised by their rotation curves, the lenses they form and their interactions with the surrounding stars and the intergalactic medium (IGM).

However, when the team measured the mass distribution of NGC 1277, they observed only the distribution of stars. From this, they concluded that DM cannot explain more than 5 per cent of the galaxy's mass within the observed radius - even though their observations suggest that there may be no DM at all. As Comerón explained in a recent IAC press release:

"This result is incompatible with currently accepted cosmological models that include dark matter. The importance of remnant 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 extracted kinematic maps that allowed us to calculate the mass distribution within the galaxy up to a radius of about 20,000 light years."

However, none of these explanations is completely satisfactory for the team.

In the near future, the team plans to investigate the mystery further by making observations with the WHT Enhanced Field Velocity Explorer (WEAVE) instrument on the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory on the island of La Palma.

If WEAVE's velocity measurements confirm that there is no DM in NGC 1277, this could cast serious doubt on alternative theories such as Modified Newtonian Dynamics (MOND). Said Trujillo:

"This discrepancy between observations and what we expect is a puzzle and even a challenge to the standard model. Although dark matter in a particular galaxy may disappear, a modified law of gravity must be universal, it cannot have exceptions, so a galaxy without dark matter is a refutation of such alternatives to dark matter."

These observations could also shed light on the galaxy's particularly massive Supermassive Black Hole (SMBH), which is roughly 17 billion solar masses, or 4,250 times the mass of Sagittarius A* (the SMBH at the centre of the Milky Way).

According to some astronomers, black holes could be the source of DM, which formed in the early Universe when DM Halos collapsed. There is also the mystery of Dark Matter Galaxies like FAST J0139+4328, which are almost entirely composed of DM.

The next generation of missions, such as the Euclid and Nancy Grace Roman space telescopes, will also provide new information by studying the expansion of the cosmos since the Big Bang. These observations aim to measure the impact of Dark Matter (and Dark Energy) on the largest cosmic scales.

The results of these and other studies will resolve the ongoing debate by revealing either that a mysterious invisible mass exists or that our understanding of gravity (as defined by General Relativity) needs to be revised.

 

Source: https://www.sciencealert.com/