Cannibalization History of Dwarf Faint Galaxy Tucana II

Galaxies are the most common thing in the universe. They can be seen everywhere. Some are dying and some are forming. Those galaxies who die sometimes dwarf galaxies our Galaxy is also surrounded by various dwarf galaxies. Now among all of these dwarf galaxies, Tucana II is kind of special and interesting. This Galaxy is 163,000 light-years away from Earth.

What makes this galaxy special is that when astrophysicist was looking into it they found out that this galaxy has this star which is very far from its center but that star is still caught up by that tiny galaxy’s gravitational pull. This fact is mesmerizing. This all suggests that Tucana II has an extended dark matter halo. Halo is a region of a galaxy where the matter is bound gravitationally. So for that star to be still in the gravitational pull of that galaxy is only possible if that galaxy has a big halo but since that galaxy is very small and dying then it must be the dark matter which bounds that star to the galaxy.

This also means that what researchers thought about galaxies formed in the early stages of the universe is wrong in some ways. Researchers from MIT said that this galaxy must have a huge amount of dark matter than they previously assumed and this also indicates that galaxies formed in earlier stages of the universe were big and had these extended halos of dark matter. They also said that this Is the very first evidence of such an imbalance in the galaxy.

The vicinity of the Tucana II ultra-faint dwarf galaxy, as imaged with the SkyMapper Telescope.
The vicinity of the Tucana II ultra-faint dwarf galaxy, as imaged with the SkyMapper Telescope. Credit: Anirudh Chiti, MIT

Tucana II has this special configuration which indicates that the galaxy must have been a result of the merger between two galaxies and one of those galaxies must have been primitive than the other.

Anna Frebel who is researching this said that it can be that one galaxy cannibalized another and then spilled its stars into the outskirts.

Based on the chemical composition of its stars Tucana II is marked as the most primitive dwarf galaxy. This dwarf galaxy has such a handful of stars with very low metal elements or heavy elements in its core. This is the reason it is deemed as a primitive faint galaxy.

Researchers are wondering whether this galaxy holds some older stars or other things that can be able to shed some light on the galaxies formed in the early stages of the universe. They also tested their idea through the sky mapper telescope which is an optical ground-based telescope housed in Australia. They told us that team used an imaging filter to spot the stars with low metal content around the Tucana II. The team ran an algorithm to filter stars with low metal content from others and the results were good.

Her research showed that outer stars move in lockstep with the inner stars of the galaxy. This suggests that Tucana II must have an extended dark halo or it won’t be able to hold those stars at its far outskirts.

Dark Matter

Dark is a hypothetical matter which we can not feel or observe. Dark matter is present in abundance in-universe making 85% of the universe. Researchers believe that galaxies are held together by it’s the concentration of the matter or by the halo of dark matter. Dark matter is crucial in galaxies without dark matter galaxies would just fly apart.

The results that Anna and her team found are that the concentration of metal in the stars is higher in inner stars. This is very odd for just a single galaxy. This brings us to the point that this is because of the galaxy’s cannibalistic history. Two galaxies merged and then a small galaxy cannibalized another galaxy or galaxies among itself. This kind of galactic cannibal exist today too but we were unsure about how the galaxies merged in earlier days.

Tucana II will eventually fall into our galaxy and will be cannibalized by Milky Way, turns out this is galaxies treat each other. Anna and her team now want to look for other faint dwarf galaxies to find more about this kind of behavior.


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