Astronomers find a galaxy in which its dark matter has been stolen



The galaxy NGC 1052-DF4 surprised scientists by having almost no dark matter to complete its stellar population. A team of astronomers recently came up with an explanation: A nearby galaxy stripped NGC 1052-DF4 of its dark matter and is currently in the process of destroying the rest of it as well.

Despite its complete invisibility, dark matter is the fundamental building block of almost everything large in the universe. When you look at a galaxy, you see all the stars and patches of glowing gas, but all that visible matter makes up less than 15% of the galaxy’s total mass. The rest is distributed in a large “halo” of dark matter. We don’t know what dark matter is, but it’s a big deal.

This had been the normal model until the discovery of the galaxy NGC 1052-DF4 in 2015. That galaxy, located about 45 million light-years away, has almost no dark matter.

This was a big conundrum, why do galaxies need halos of dark matter to even start forming, so how could all those stars and gases bond together without a dark side?

A team of astronomers used a combination of ground-based observations and the Hubble Space Telescope to examine NGC 1052-DF4 in more detail, particularly by looking at globular clusters. Globular clusters are small, dense clusters that orbit around a galaxy (the Milky Way has over 150).

The astronomers found that the globular clusters orbiting NGC 1052-DF4 weren’t in all kinds of random orbits, but tended to be aligned with each other. Furthermore, a closer examination of the stars in NGC 1052-DF4 revealed the presence of tidal tails, which are long streams of stars extending in opposite directions of a galaxy.

Tidal tails only appear when a galaxy gets too close to a neighbor, and globular clusters have shown who was responsible: NGC 1035.

It appears that NGC 1052-DF4 came into conflict with NGC 1035 and NGC 1035 won. Through the interaction, NGC 1035 removed the loose dark matter of the halo, leaving behind only the dense core of stars in NGC 1052-DF4.

But this too is about to end. NGC 1035 is not ready and will soon tear the entire galaxy apart. We happened to see him in the middle of the act.


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