In addition to the billion stars of the Milky Way, the Gaia spacecraft (ESA) also observes extragalactic objects. Its automatic alert system notifies astronomers whenever it finds a transient event. A group of astronomers have found that by modifying an existing automated system, Gaia can be used to detect hundreds of specific transients at the centers of galaxies. They found about 480 transients in about one year. Their new method will be implemented in the system as soon as possible, allowing astronomers to determine the nature of these events. The findings will be published in the November issue of the Royal Astronomical Society's monthly notices.
In 2013, ESA launched its Gaia spacecraft to measure the location of billions of stars in the Milky Way and tens of millions of galaxies. Each position in the sky is included in the survey of the device at least once a month, and a total of about 70 times during the entire mission. This allows the spacecraft to detect transient events such as supermassive black holes tearing stars apart or stars exploding like a supernova. Gaia notices the change in brightness even when he returns to the same area of the sky a month later. Recently, a group of astronomers from SRON, the University of Radboud and the University of Cambridge reported about 500 transients occurring in the centers of galaxies in one year.
Astronomers Zuzanna Kostrzeva-Rutkowska, Peter Jonker (both associated with SRON and Radbud University), Simon Hodgkin and others have explored Gaia's databases, working on transient events around galactic nuclei between July 2016 and June 2017. They used the Sloan Digital Sky Survey Release 12 catalog of galaxies and special mathematical tools. The new tool allows researchers to identify rare luminous events taking place in the centers of galaxies. As a result, scientists found 480 new events.
The main explanation for most of the events is that the supermassive black holes that inhabit the cores of galaxies suddenly become much more active as the amount of gas entering the black hole splashes out and illuminates the black hole's cramped environment. This fresh 'fuel' can be extracted from a star that has been torn apart by the black hole's massive gravitational pull.
With the help of the William Herschel telescope in La Palma, Peter Jonker with Zuzanna Kostzheva-Rutkowska and other scientists from his group were able to decipher the nature of 480 new transients.
