Astronomers have discovered a cluster of tiny galaxies at a distance of 3 million light-years from Earth, including — the smallest ever seen.
This galaxy is called Andromeda XXXV and, together with other similar galaxies, orbits the neighboring Andromeda galaxy. The discovery of this tiny galaxy could change the way scientists think about the evolution of the cosmos.
The thing is that these tiny galaxies should have disappeared under the conditions of ultra-high temperatures and density of the early Universe. But somehow they managed to survive.
«These are fully functional galaxies, but they are about a millionth the size of the Milky Way. It’s like having a fully functional human being the size of a grain of rice», — explains Eric Bell, a member of the team of astronomers who made the discovery, a professor at the University of Michigan.
Astronomers have discovered dwarf galaxies before. Dozens of smaller satellite galaxies also orbit our Milky Way galaxy. However, there is still much that scientists do not know about these tiny galaxies because, given their size, they emit much less light than larger galaxies. This makes them difficult to spot and investigate.
Many tiny galaxies have been discovered orbiting the Milky Way, but so far it has been incredibly difficult to detect similar galaxies around our neighbors. Until recently, the dwarf galaxies that are satellites of the Milky Way were our only source of information about small galaxies.
Small galaxies had already been observed around Andromeda, but they were quite large in size and quite bright.
To detect tiny galaxies around Andromeda, astronomer Marcos Arias from the University of Michigan and his colleagues studied various catalogs of astronomical objects. The scientists also took advantage of information from the «Hubble» telescope, which significantly reduced their search time. They made sure that the Andromeda XXXV galaxy is not only a satellite galaxy, but also so small that it is likely to change the theory of galaxy evolution.
What surprised astronomers about the Andromeda XXXV galaxy
One of the key questions in the evolution of galaxies is how long the periods of star formation in them last. This seemed to be the main difference between the dwarf galaxies around Andromeda and The Milky Way.
«Most of the Milky Way satellites have very old stellar populations. They stopped forming stars about 10 billion years ago. We can see that similar satellites around Andromeda were capable of forming stars several billion years ago — about 6 billion years», — Marcos Arias notes.
For the formation of stars, there must be sufficient amount of gas and dust. When the gas stops flowing, star formation stops. Did the star formation stop when the gas in dwarf galaxies ran out on its own, or when the gas was gravitationally removed by a large galaxy? In the galaxies around the Milky Way, the gas was exhausted by itself. However, the tiny galaxies around Andromeda seem to have stopped star formation because of their own parent galaxy.
«It’s a bit dark, but did they decay on their own or were they pushed to do so? It seems that these galaxies were pushed. Thanks to this, we learned something qualitatively new from them about the formation of galaxies», — emphasized Eric Bell.
Astronomers were particularly interested in the long period of star formation in the Andromeda XXXV galaxy. The early Universe was dominated by very high temperature and density. However, the period of inflation that began after the Big Bang continued, the Universe expanded and became increasingly cold. After the formation of hydrogen and helium atoms, the first stars began to form and gather into galaxies.
These galaxies released large amounts of energy into space and heated the Universe. This energy destroyed small galaxies in the form of heat. According to scientists, this heat burned off the gas needed to form stars in these dwarf galaxies. However, somehow Andromeda XXXV managed to survive.
«We thought they should all burn up because the Universe was like a vat of boiling oil. We thought that this galaxy would lose all its gas, but apparently that didn’t happen, because this galaxy is about 20 thousand solar masses, and yet it was perfectly capable of forming stars for a few extra billion years», — said Eric Bell.
Astronomers still do not know how the Andromeda XXXV galaxy managed to survive in such conditions. NASA and other leading global agencies are planning missions to detect new dwarf galaxies around larger ones. But there is a high probability that the solution will open up new questions, as happened with the discovery of Andromeda XXXV.
Source: Space.com; LiveScience
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