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A huge discovery that is incompatible with our current theories of galaxy and dark matter formation may well have been solved.
After a new analysis, astronomers have determined that NGC1052-DF2 – discovered last year as containing absolutely no dark matter – is much closer to us than previous calculations. Which means that there is probably some dark matter after all.
Dark matter is a big question mark on the Universe. We do not know what it is, and we can not detect it directly, but we know that there is something that creates the same effect as the mass in the Universe.
Objects in galaxies, for example, move faster than they should according to the mass that we can detect directly; an undetectable force – a dark matter, if you like – generates more gravity than we can account for with normal matter.
These things are fundamental to our understanding of the Universe. We think that it helped stars and galaxies to form from the primordial soup that existed just after the Big Bang, and that it prevents the contents of galaxies from flying into the galaxy. # 39; space.
And our galaxy formation model depends on it.
"For decades, we thought that galaxies began life as dark matter patches," said astronomer Pieter van Dokkum of Yale University last year.
"After that, all the rest happens: the gas falls into the halo of dark matter, it turns into stars, then slowly accumulate, then you end up with galaxies like the Milky Way." NGC1052-DF2 challenge standard ideas about how we think galaxies are formed. "
Dark matter therefore seems to be a fairly critical ingredient and indeed, until the discovery of NGC1052-DF2, each galaxy seemed to have at least a part of it. In fact, most seem to have more dark matter than normal matter.
This is why an international team of researchers led by the Instituto de Astrofísica de Canarias (IAC) decided to take a closer look. And they found that all the abnormal measurements of previous research that indicated an absence of dark matter depended on the distance that separated them from the galaxy, 64 million light-years away.
It gave them something to work on. Using five separate methods, including the Hubble Space Telescope Photometry and the Gemini Observatory, they recalculated the distance to NGC1052-DF2.
Each method gave the same result – NGC1052-DF2 is much closer to 64 million light-years. According to the multiple calculations of the team, a more accurate distance would be about 42 million light years away.
Based on this new distance, the mass of the galaxy is about half of what was thought to be before – and the mass of stars is only a quarter of what the previous analysis suggested.
Thus, not only does the galaxy itself have less mass, but the proportion of normal matter in this mass is smaller. This implies that the rest must be made up – you guessed it – of dark matter.
In addition to the calculations, the lack of dark matter had already been deduced based on the slow movement of star clusters in the galaxy. With a reduced overall mass in the galaxy, this speed of movement is actually rather normal.
"With this revised distance," the researchers wrote in their article, "the galaxy appears to be a fairly ordinary low-light galaxy, with plenty of space for dark matter."
Now, this is not the end of the story. We do not yet know if a similar problem also concerns NGC1052-DF4, a galaxy whose number is close to DF2 located about 63 million light-years away, which van Dokkum's team has discovered to have no dark matter.
Look at this space: After all, science at work is a beautiful thing.
The research was published in the Monthly Notices from the Royal Astronomical Society.
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