The NASA/ESA Hubble Space Telescope has captured incredible images of two small, ancient galaxies in the constellation of Pisces. According to astronomers, these two galaxies have lived in isolation for billions of years and are just now beginning to make new stars.
These Hubble images show small, ancient galaxies Pisces A (left) and Pisces B. Image credit: NASA / ESA / E. Tollerud, STScI.
The Hubble observations suggest that the galaxies, called Pisces A and B, are late bloomers because they have spent most of their existence in the Local Void, a 150 million-light-year-wide region of the Universe sparsely populated with galaxies.
“These Hubble images may be snapshots of what present-day dwarf galaxies may have been like at earlier epochs,” said Dr. Erik Tollerud of the Space Telescope Science Institute.
“Studying these and other similar galaxies can provide further clues to dwarf galaxy formation and evolution.”
Pisces A is approximately 19 million light-years away and Pisces B is about 30 million light-years from Earth.
Each galaxy contains about 10 million stars, among which only 20 to 30 are very young blue stars.
Dr. Tollerud and co-authors estimate that less than 100 million years ago, the galaxies doubled their star-formation rate.
According to scientists, dwarf galaxies like Pisces A and Pisces B are the building blocks from which larger galaxies were formed billions of years ago in the early Universe.
Inhabiting a sparse desert of largely empty space for most of the Universe’s history, Pisces A and B avoided that busy construction period.
“These galaxies may have spent most of their history in the void. If this is true, the void environment would have slowed their evolution,” Dr. Tollerud said.
“Evidence for the galaxies’ void address is that their hydrogen content is somewhat high relative to similar galaxies.”
“In the past, galaxies contained higher concentrations of hydrogen, the fuel needed to make stars.”
“But these galaxies seem to retain that more primitive composition, rather than the enriched composition of contemporary galaxies, due to a less vigorous history of star formation.”
“The galaxies also are quite compact relative to the typical star-forming galaxies in our galactic neighborhood.”
Now Pisces A and Pisces B have moved into a region crowded with galaxies and full of intergalactic gas.
In 2015, Dr. Tollerud and his colleagues spotted the galaxies by using radio telescopes in a unique survey to measure the hydrogen content in our Milky Way Galaxy.
The observations captured thousands of small blobs of dense hydrogen gas. Most of them are gas clouds within our galaxy, but astronomers identified 30 to 50 of those blobs as possible galaxies.
The team then used the WIYN telescope to study 15 of the most promising candidates in visible light.
Based on those observations, the astronomers selected the two that are the most likely candidates to be nearby galaxies and analyzed them with Hubble’s Advanced Camera for Surveys.
Hubble’s sharp vision helped the team confirm that both of them are dwarf galaxies.
The team’s findings have been accepted for publication in an upcoming edition of the Astrophysical Journal. The article is also publicly available at arXiv.org.
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Erik J. Tollerud et al. 2016. HST Imaging of the Local Volume Dwarf Galaxies Pisces A&B: Prototypes for Local Group Dwarfs. ApJ, accepted for publication; arXiv: 1607.03487
