Astronomers Discover the Most Diffuse and Lowest Surface Brightness Galaxy Ever Seen
A ‘ghost’ also known as a low surface brightness dwarf galaxy has been unexpectedly detected by Astronomers on the outer edges of our own galaxy.
An international group of astronomers discovered the most diffuse and lowest surface brightness galaxy ever spotted after scanning the most recent batch of data from the European Space Agency’s (ESA) Gaia spacecraft. The ‘ghost’ is now called Antlia 2, after the constellation where it lies, it’s officially a new satellite galaxy of the Milky Way.
Gabriel Torrealba, the team lead and an astrophysicist at Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) stated that it’s unclear how this galaxy came to be so ghostly.
Around one third the diameter of the Milky Way, Torrealba remarks that Antlia 2 is approximately the same size as the nearby Large Magellanic Cloud (LMC) but shines about 10,000 times fainter.
These kinds of low surface brightness galaxies have very low star-forming rates and generate very few if any supernovae.
One of the reasons Antilia 2 had not been detected until now was simply that it lies in an inherently tricky part of the galactic plane to observe. It’s an area full of dust and an overabundance of bright stars close to the galactic center.
However, the team was able to use around a hundred old and metal-poor pulsating, so-called ‘RR Lyrae’ stars to examine inside and ultimately identify Antlia 2 in this galactic zone of avoidance.
Torrealba explained that the zone of avoidance is essentially the part of the sky obscured by the Milky Way’s disk as seen from the Earth. The disk of the Milky Way has a lot of gas and stars, making it extremely crowded and complicated.
Torrealba added that due to this complexity performing any kind of study there becomes very hard to do. However, Gaia is capable of digging into the Zone of Avoidance since it provides high-quality proper motions of stars behind the central disk of our Milky Way galaxy. Meaning, it is able to track stars as they travel across the celestial sphere.
In the journal Monthly Notices of the Royal Astronomical Society, the team states that situated behind the galactic disk Antlia 2 was discovered using data from Gaia’s latest Data Release 2 (DR-2) in addition to follow-up ground-based observations with the Anglo-Australian Telescope in Australia. Although it is clearly a satellite, it never comes closer than approximately 130,000 light years from the Milky Way.
Torrealba explained that Antlia 2 is likely to be one of the oldest dwarf galaxies in the universe, however, he and his team are still trying to figure out how it became so diffuse.
One reason could be that Antlia 2 was much more massive in the past, and as it fell into the Milky Way, it lost its mass and became more diffuse, said Torrealba.
But one issue with this idea, according to Torrealba, is that instead of growing, galaxies tend to shrink at the same time they lose stars.
As of now, there seems to be no limit on how diffuse and low surface bright a galaxy can become, according to Stacy McGaugh, an astronomer at Case Western Reserve University in Cleveland, who wasn’t involved in the study.
One of the biggest mysteries is just how many more of these dwarf galaxies are lurking around our own Milky Way. The authors remark that our galaxy may still have between one and three undetected dwarf satellite galaxies, each with 100,000 stellar masses or more.
The post Astronomers Discover the Most Diffuse and Lowest Surface Brightness Galaxy Ever Seenappeared first on Asgardia.
Learn more: Asgardia Space News
