JOIN USBengaluru scientists discover ghost galaxy with Astrosat data
Astrophysicists from Bengaluru have discovered a galaxy with a “ghost-like appearance” that can offer vital clues to one of the long-standing cosmic mysteries – how the visible matter is distributed in the universe.
Three researchers at the Indian Institute of Astrophysics, Bangalore collaborating with a French scientist have discovered a faint but star-forming galaxy, around 136 million light-years away which was so far undetected since it lies in front of a much brighter galaxy.
"In the optical image, the galaxy has a ghost-like appearance because of the blue emission from its outer sphere. It has a low disk density, but the inner disk shows star formation, which helped its detection in UV and optical images,” Mousumi Das, a senior scientist at the IIA and one of the team members, told DH.
When Das, her student Jyoti Yadav, another IIA scientist Sudhanshu Barway and Francoise Combes from College de France, Chaire Galaxies et Cosmologie, Paris began observing a known galaxy (NGC 6902A) in the ultra-violet spectra, they were surprised to find a faint emission from the star formation region of a galaxy.
They continued their observation in the UV and visible spectra and spotted a hidden galaxy with a very low luminosity. The new galaxy was named UVIT J2022 as the data came from Astrosat’s Ultraviolet Imaging Telescope.
When the IIA team measured the distance between the known galaxy and the faint star-forming regions, they found the latter at a distance of 136 million light-years, whereas the distance of NGC 6902A is 825 million light-years.
"Most diffuse galaxies don’t have star formation regions in the central part. In that way, it's an unusual galaxy,” Das said, observing there could be more such galaxies that have been wrongly interpreted as interacting galaxies due to their superposition with foreground or background galaxies.
Modern optical telescopes are sensitive enough to detect galaxies that are extremely faint. Such galaxies are called low surface brightness galaxies or ultra-diffuse galaxies and have a surface brightness that is at least ten times fainter than the surrounding night sky.
Such faint galaxies may account for up to 15 per cent of the mass of the universe. But they are difficult to detect because of their inherent low luminosities. An accurate census of such faint galaxies is essential to measure the total mass of all objects made of normal atomic matter (stars and gas) in the universe.
The discovery opens up a new window to look for the missing masses in the universe. Cosmological studies suggest baryonic matter (the visible matter) should make 5 per cent of the universe's mass. The rest comes from dark matter and dark energy.
“We still do not have a clear understanding about the 5 per cent of the baryonic content present in the universe. Such faint galaxies can act as a link for understanding the origin of missing baryons as they may contribute significantly to the visible mass in the universe,” she said.
The study appeared in the journal ‘Astronomy & Astrophysics'.
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