There is a supermassive black hole at the heart of the Milky Way Galaxy. It is called Sagittarius A* and scientists believe that it is about 4 million times the mass of the sun.

However, how did it become so big?

A team of astronomers from the Tel Aviv University believes that they have unlocked the secret behind the monstrous size of supermassive black holes. In a paper published in the journal Nature Astronomy, the team discussed a new way of "feeding" that could explain how supermassive black holes get so enormous.

Colossal Mystery No More

A black hole gains mass by gobbling up matter from beyond its event horizon — the area in which the gravitational pull is so strong that nothing, not even light, can escape. For a supermassive black hole, the rules are different. There a few theories about how a supermassive black hole forms and grow into impossible proportions, but none have been conclusive so far.

According to the team led by Benny Trakhtenbrot and Iair Arcavi, the missing piece of the puzzle lies in the AT 2017bgt.

In February 2017, the All Sky Automated Survey for Supernovae discovered AT 2017bgt. They initially thought that it was a star swallowing event or a tidal disruption because of how bright it suddenly became, but immediately, the astronomers of TAU's Raymond & Beverly Sackler School of Physics and Astronomy found that something unusual was happening.

"We followed this event for more than a year with telescopes on Earth and in space, and what we saw did not match anything we had seen before," said Arcavi.

Researchers from all over the world, including the United States and the United Kingdom, took part in the observation and analysis of the event. The team used three different space telescopes to watch the AT 2017bgt.

They observed that the optical and ultraviolet emission around the black hole increased by about 50 percent in only a year. The X-ray emission also grew by several factors before dying down.

A Black Hole Feeding Frenzy

The astronomers concluded that some supermassive black holes are triggered to grow by devouring a large amount of gas, an observation that matched a theoretical prediction made by Hagai Netzer, a member of the research team, in the 80s.

"We had predicted back in the 1980s that a black hole swallowing gas from its surroundings could produce the elements of light seen here," explained Netzer. "This new result is the first time the process was seen in practice."

The team reported two other black holes that have been "switched on." Both share similar emissions observed from AT 2017bgt.