A research team led by Cardiff University scientists claim to have made a great stride towards understanding how a supermassive black hole (SMBH) is born.
The scientists used a new technique that allowed them to zoom in on one of the cosmic giants in never-before-seen detail.
'Direct collapse' or gradual growth?
Scientists have long debated whether SMBHs were formed in a process called a 'direct collapse' brought on by the extreme conditions of the universe shortly after the big bang, or whether they came into existence much later resulting from the death of massive stars.
If SMBHs were formed by the 'direct collapse' process, they would be born with extremely large masses and would have a fixed minimum size. If they were formed by the death of massive stars then SMBHs would start off relatively small — roughly 100 times the mass of our Sun — before gradually growing larger by feeding on the gas clouds and stars in their vicinity.
Astronomers have long been trying to decipher this problem by searching for the lowest mass SMBHs — which are seen as the missing link in the equation.
Studying 'Mirach's Ghost'
In a new study, published in the Monthly Notices of the Royal Astronomical Society, the Cardiff University team has revealed one of the lowest-mass SMBHs ever observed.
The SMBH, which weighs less than one million times the mass of our sun, was observed in the center of a nearby galaxy called NGC 404, which is also known as "Mirach's Ghost" due to a ghostly shadow cast by a very bright star called Mirach.
The findings were made via a new technique that was utilized while observing Mirach's Ghost with the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA is located on the Chajnantor plateau in the Chilean Andes and is used to study light from some of the coldest objects in the visible Universe.
The ALMA telescope allowed the team to visualize the gas clouds at the center of the galaxy in detail only 1.5 light-years across, making their visualization one of the highest resolution maps of gas ever made of another galaxy.
Searching a supermassive black hole's minimum mass
By observing the galaxy with such unprecedented high resolution, the team was able to put a decade's worth of conflicting results to bed and, in doing so reveal the true nature of the SMBH at the heart of Mirach's Ghost.
"Our study demonstrates that with this new technique we can really begin to explore both the properties and origins of these mysterious objects," Dr. Tim Davis from Cardiff University's School of Physics and Astronomy said in a press release. Davis did emphasize that, "if there is a minimum mass for a supermassive black hole, we haven't found it yet."
Davis explained that the SMBH in Mirach's Ghost appears to have a mass within the range that is predicted by models of the 'direct collapse' theory.
"We know it is currently active and swallowing gas, so some of the more extreme 'direct collapse' models that only make very massive SMBHs cannot be true," Davis continued.
"This on its own is not enough to definitively tell the difference between the 'seed' picture and 'direct collapse', we need to understand the statistics for that — but this is a massive step in the right direction."
The next step for the researchers will be to continue to use their new technique to study known supermassive black holes at the center of other galaxies. In doing so, they might finally reveal the true origin of those enigmatic cosmic giants.