Newly-Discovered Black Holes In Dwarf Galaxies Could Explain How They're Formed

Researchers at the University of North Carolina at Chapel Hill have discovered a treasure trove of massive black holes, hidden inside dwarf galaxies, offering us a glimpse into how the supermassive black hole that¡¯s at the centre of the Milky Way came into existence, reveals a report by Phys.org.

Representational Image: NASA

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The Milky Way is believed to be formed by the fusing of several dwarf galaxies and each dwarf galaxy that falls in, also brings along with it a central massive black hole, which is considerably more than the mass of our sun, only destined to be swallowed by the supermassive black hole at the centre.

But researchers don¡¯t really know how often dwarf galaxies contain a massive black hole. However, the new study has revealed that the massive black holes are many times more common in dwarf galaxies than previously believed.

To the unaware, black holes are usually detected when they actively start growing by ingesting gas and stardust, making them glow. At this time, they also exude distinctive high-energy radiation, but so do newborn stars.

So to differentiate between the two, astronomers have traditionally used diagnostic tests that rely on detailed features of each galaxy's visible light when spread out into a spectrum like a rainbow.

However, while applying these traditional methods to galaxy survey data, they saw that galaxies were sending mixed messages -- two tests showed black holes growing while a third would show it¡¯s just a star formation.

UNC-Chapel Hill Professor Sheila Kannappan, the co-author of the study, explained, "Previous work had just rejected ambiguous cases like these from statistical analysis, but I had a hunch they might be undiscovered black holes in dwarf galaxies."

According to Kannappan, the third sometimes contradictory test was more sensitive than the other two to typical properties of dwarf galaxies -- their elemental composition and their high rate of forming new stars.

Another study co-author, Chris Richardson, an associate professor at Elon University confirmed with the help of theoretical simulations that the mixed-message test results very well matched what theory would predict for primordial composition, a highly star-forming dwarf galaxy consisting of a growing massive black hole.

NASA

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Researchers took on the challenge of creating a new census of growing black holes, with attention to both traditional and mixed message types. They looked at published measurements of visible light spectral features to test for black holes in thousands of galaxies found in the surveys led by Kannappan, RESOLVE and ECO. The surveys included UV and radio data that are perfect for studying star formation. They also possess an unusual design -- RESOLVE and ECO are complete inventories of huge volumes of the present-day universe that are abundant in dwarf galaxies.

Mugdha Polimera, lead author of the study and a UNC-Chapel Hill PhD student explained, "It was important to me that we didn't bias our black hole search toward dwarf galaxies. But in looking at the whole census, I found that the new type of growing black holes almost always showed up in dwarfs. I was taken aback by the numbers when I first saw them."

Researchers saw over 80 percent of all growing black holes in dwarf galaxies to belong to a new type.

Kannappan added, "We're still pinching ourselves. We're excited to pursue a zillion follow-up ideas. The black holes we've found are the basic building blocks of supermassive black holes like the one in our own Milky Way. There's so much we want to learn about them."

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