Astronomers at Universidad de Chile determined a method to estimate the masses of supermassive black holes

Thursday, July 21, 2016

Julián Mejía, Ph.D student in Astronomy.
Paulina Lira, astrónomer of the U. of Chile.

Even though scientist have been able to decipher many aspects of black holes, there are still many mysteries that have not been unveiled about these objects. Those mysteries are even bigger when scientist try to explain ‘supermassive’ black holes, those with masses larger than one million solar masses.

Up to date, there is general agreement among the scientific community on the fact that every single galaxy, including our own Milky Way, hosts one supermassive black hole at their center. Consequently, it is crucial to precisely determine the masses of these objects to be able to understand their influence in their local and global environments.

Paulina Lira, associate professor of the Astronomy Department at Universidad de Chile (DAS) and coauthor of the study, explains that when these objects are inactive they can only gravitationally affect surrounding material within a tiny volume of space. However, when one of these objects becomes ‘active’ by consuming its surrounding material, its effect can be felt at much larger distances. “The material falling into the black hole forms a disc or, in other words, an incandescent whirlwind that can shine as much as all the stars of the host galaxy combined. This is a monumental amount energy. Such energy is not only released in form of radiation but also in form of very energetic jets of material traveling at almost the speed of light. This ejected material can travel up to the edge of the galaxy and even further away. These jets usually heat up the galactic environment and may quench the formation of stars in the galaxy.

A team of international astronomers, including researchers from DAS, have been able to establish a precise and reliable method to estimate the masses of these objects in active galaxies (i.e. galaxies with supermassive black holes at their centers that are consuming material) by means of the information coming from the gas that is close to the supermassive black hole.

Julián Mejía, first author of the research and PhD student at DAS, explains that ‘the disc of incandescent material is being devoured by the supermassive black hole (just like in the Interstellar movie!). Around the disc, there are some clouds of gas that are illuminated by the light coming from the disc. From the analysis of the spectrum of these clouds it is possible to estimate their velocity and distance to the black hole. After combining such information (the velocity and distance) it is possible to derive the black hole mass’.

The scientist states that the main finding of their research is that the estimated masses become more reliable the more distant the clouds are from the disc. One possible explanation for this is that the nearest clouds are more likely to be disturbed by material from the disc that comes in the form of winds " he says (an explanatory video can be found at Credits: Ricardo Ramirez).

The mass of supermassive black holes can be 10 to 1000 million times the mass of the Sun and astronomers cannot yet figure out how they managed to grow that much. "To reconstruct their evolution over time and determine how they grew we need first to look at very distant regions of the universe and measure their masses as accurate as possible. And not only that. Supermassive black holes show a strong correlation between their masses and the masses of their host galaxies. Typically, the mass of these objects corresponds to only 1% of the total mass of the galaxy. How was this correlation happened? At what point in the life of the universe it was first established? Those are questions that we cannot answer just yet. As a first step we need to accurately measure the masses of the central supermassive black holes. The work we are publishing now explores in detail into the methods to do this accurately”, the astronomy professor at the University of Chile explains.

The results of this research used 80 hours of the X-Shooter instrument at the VLT telescope that is located in the region of Antofagasta, Chile. The work was published in the recent edition of July 21 of MNRAS (Monthly Notices of the Royal Astronomical Society), a journal with one of the highest impact factors in astronomy.

The next step in the research is to study how the mass of the supermassive black holes, its intrinsic rotation and the rate at which they devour matter, determine the properties of their surrounding material.