Astronomers solve a Dark Matter mystery, saving our Galaxy Formation model


A small mysterious galaxy 44 million light years away is finally revealing its secrets. As revealed last year that there is an extremely small amount of dark matter, the galaxy NGC 1052-DF4 has presented a significant challenge to our model of galaxy formation.

Those models live on yet another day. According to new research, NGC 1052-DF4 is actually lacking in dark matter – but only because another galaxy nearby dropped it.

“Dark Matter is not because it has already been removed,” said astrophysicist Miria Montes of the University of New South Wales in Australia and the Space Telescope Science Institute.

“We found that the gravitational pull from the nearby massive galaxy NGC1035 is removing its stars – and dark matter.”

(Montes et al., ApJ, 2020)

The discovery of NGC 1052-DF4 (or DF4 for short) was announced last year, and was immediately a deli of an astronomical pickle. It was the second galaxy of its type – a faint, ultra-diffuse galaxy, or UDF – to be found to be seriously dark. The first was NGC 1052-DF2 (DF2), and DF4 represented a confirmation that insufficient dark matter galaxies exist.

The problem was that, according to our current model, galaxies required dark matter in the first place.

We do not know what Dark Matter is, and we cannot detect it directly, but we do know that most galaxies have higher gravity than their normal, detectable matter. There is some hidden mass in the universe that is forming that extra bridge, and without it, according to our understanding of galaxy formation, there would not be enough gravity for the collapse of matter to form infant galaxies.

The case was approaching a proposal, when a team of astronomers discovered that DF2 was actually much closer to us than previously thought. This meant that it had a much lower mass than the initial calculations suggested, and the proportion of normal matter was very low. Once the calculation was completed based on the modified distance, DF2 contained a normal amount of dark matter.

He then focused his attention on DF4. It, too, seemed so close … but something was still not quite right. The velocities of the clusters of stars inside the galaxy were still suggesting that there was a far deeper case than it should have been.

The faint galaxy is very difficult to see, so Montes and his colleagues book time on some of the world’s most powerful telescopes to see why they can understand.

Using the IAC80 telescope, the Gran Telescopio canaria, and the Hubble Space Telescope, they found that the stars were being ejected from DF4, corresponding to interactions with the much larger spiral galaxy NGC 1035. This process, whereby a large body gravity “disrupts”. A short, known as tidal disintegration.

“Preliminary papers showed that the galaxy has a very ‘relaxed’ symmetric shape, suggesting that no external forces were disturbing it,” Monte said.

“But our darker images show that this galaxy is actually being influenced by its neighboring galaxy – it’s just caught at the beginning of the conversation. The inner part of the galaxy retains its shape, but the outer, faintest The parts are where you see them. ” ‘Tidal Tails’: Stars that have already separated from the Milky Way. “

df4 tailTidal tail found streaming out of DF4. (Montes et al., ApJ, 2020)

Monte stated that since dark matter surrounds galaxies in a large halo, this tidal stripping will affect most of the dark matter in the smaller galaxy. The stars begin to shrink only after the galaxy is less than 10 to 15 percent of its total mass.

This is in line with the team’s comments. UDFs have a high proportion of dark matter – about 99 percent of the galaxy’s total mass. In the case of DF4, the team estimated that dark matter makes up only one percent of the total mass.

Because Dark Matter is basically the gravitational glue that holds galaxies together, it also means that the time of DF4 in this universe is limited.

NGC1052-DF4 is being freed in deep space by at least some stars by the large system surrounding NGC1035. “

But at least we don’t have to go back to the drawing board on the creation of the galaxy.

The research has been published in The Astrophysical Journal.

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