[ad_1]
A mysterious little galaxy 44 million light years away is finally revealing its secrets. Revealed last year to have an incredibly low amount of dark matter, the galaxy NGC 1052-DF4 posed a daunting challenge to our galaxy formation models.
These models live yet another day. NGC 1052-DF4 is indeed lacking in dark matter – but only because another neighboring galaxy has slashed it, according to new research.
“The dark matter is not there because it has already been removed,” said astrophysicist Mireia Montes of the University of New South Wales in Australia and the Space Telescope Science Institute.
“We have found that the gravitational pull of the nearby massive galaxy NGC1035 removes 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 it was immediately a dilly of an astronomical pickle. It was the second such galaxy – a weak and ultra-diffuse galaxy, or UDF – to be found to be seriously depleted of dark matter. The first was NGC 1052-DF2 (DF2), and DF4 represented confirmation that galaxies with insufficient dark matter could exist.
The problem was, according to our current models, dark matter is needed for galaxies to form in the first place.
We don’t know what dark matter is and we can’t detect it directly, but we do know that most galaxies have a lot more gravity than their normal detectable matter could create. There is a hidden mass in the Universe that creates this additional attraction, and without it, according to our understanding of the formation of galaxies, there would not be enough gravity for matter to collapse to form baby galaxies. .
The question seemed to be approaching a resolution when a team of astrophysicists discovered that DF2 was actually much closer to us than we thought. This meant that it had much less mass than initial calculations suggested and that the proportion of normal matter was much lower. After the calculations based on the revised distance were completed, DF2 had a fairly normal amount of dark matter.
Then they focused their attention on DF4. It also seemed to be a lot closer… but something was still wrong. The velocities of star clusters inside the galaxy always suggested that there was much less dark matter than there should be.
The faint galaxy is very difficult to see, so Montes and his colleagues set aside time on some of the most powerful telescopes in the world to see if they could figure out why.
Using the IAC80 telescope, the Gran Telescopio Canarias, and the Hubble Space Telescope, they detected stars being removed from DF4, which corresponds to an interaction with the much larger spiral galaxy NGC 1035. smaller, is known as tidal disturbance.
“Early papers showed the galaxy to have a very ‘relaxed’ symmetrical shape, suggesting that no outside force was disturbing it,” Montes said.
“But our deep images show that this galaxy is in fact affected by its neighboring galaxy – it’s just taken at the start of the interaction. The inner part of the galaxy keeps its shape, but the paler outer parts are where you get them. see. ‘tidal tails’: stars that have already been separated from the galaxy. “
The tide tails were found exiting DF4. (Montes et al., ApJ, 2020)
As dark matter surrounds galaxies in a large halo, this tidal stripping would remove most of the dark matter from the small galaxy before affecting the stars, Montes noted. Stars do not begin to be stripped until the dark matter content drops below 10 to 15% of the total mass of the galaxy.
This matches the team’s observations. UDFs tend to contain a high proportion of dark matter – about 99% of the total mass of the galaxy. In the case of DF4, the team estimated that dark matter was only one percent of the total mass.
Because dark matter is basically the gravitational glue that holds galaxies together, it also means DF4’s time in this universe is limited.
“Over time,” said astrophysicist Ignacio Trujillo of the Instituto de Astrofísica de Canarias, “NGC1052-DF4 will be cannibalized by the large system around NGC1035, with at least some of their stars floating freely in deep space. . “
But at least we don’t have to go back to the drawing board on how galaxies were formed.
The research was published in The astrophysical journal.
[ad_2]
Source link