Using three of the largest telescopes around the world - namely, the Large Binocular Telescope (LBT), the ESO Very Large Telescope (VLT), and the W.M. Keck Observatory Telescope - astronomers found a Large Scale Structure made of six galaxies lying around a massive galaxy harboring a supermassive black hole (SMBH), the first time such a close grouping has been seen within the first billion years of the Universe. The finding helps us better understand how supermassive black holes, one of which exists at the center of our Milky Way, formed and grew to their enormous sizes. It supports the theory that black holes can grow quickly within large web-like structures, which contain plenty of gas to fuel them.
The Large Scale Structure with six galaxies around the Quasar/SMBH (Artist view - Credit: ESO)
“This research was mainly driven by the desire to understand some of the most challenging astronomical objects — supermassive black holes in the early Universe. These are extreme systems and, to date, we have no good explanation for their existence,” says Marco Mignoli, an astronomer at the National Institute for Astrophysics (INAF) in Bologna, Italy and lead-author of the new research published today in Astronomy & Astrophysics Letters.
The new observations revealed multiple galaxies surrounding a supermassive black hole, lying in a cosmic ‘spider web’ of gas and galaxies extending over 300 times the size of the Milky Way. “The cosmic web filaments are like spider-web threads,” explains Mignoli. “The galaxies stand and grow where the filaments cross, and streams of gas — available to fuel the galaxies and the central supermassive black hole — can flow along the filaments”.
Mignoli and his team found this large web-like structure with a black hole of one billion solar masses at a time when the Universe was only 0.9 billion years old. “Our work has placed an important piece in the largely incomplete puzzle that is the formation and growth of such extreme, yet relatively abundant, objects so quickly after the Big Bang,” says co-author Roberto Gilli, also an astronomer at INAF in Bologna.
The very first black holes, thought to have formed from the collapse of the first stars, must have grown very fast to reach masses of a billion Suns within the first 0.9 billion years of the Universe’s life. But astronomers have struggled to explain how sufficiently large amounts of ‘black hole fuel’ could be available to help these objects grow to such enormous sizes in a short time. The newfound structure offers a likely explanation: the large amounts of gas in it provide the fuel the central black hole needs to quickly become a supermassive giant.
But how did such large web-like structures form in the first place? Astronomers think giant halos of mysterious dark matter are key. These large areas of invisible matter are thought to attract huge amounts of gas in the early Universe; together, the gas and invisible matter form the web-like structures where galaxies and black holes can evolve.
“Our finding lends support to the idea that the most distant and massive black holes form and grow within massive dark matter halos in large-scale structures, and that the absence of earlier detections of such structures was likely due to observational limitations,” says Colin Norman of Johns Hopkins University in Baltimore, US, also a co-author on the study.
The galaxies now detected are some of the faintest that current astronomical instruments can observe. This discovery required observations from the largest optical telescopes available. The hunt started eight years ago, when the team - using the superb imaging quality of the Large Binocular Camera (LBC) mounted on the LBT - selected about twenty galaxies with peculiar photometric colors that could be possible neighbors of the central black hole. In the following years, using spectrographs mounted on the LBT Observatory (MODS), the ESO VLT (FORS2), and the Keck Observatory (DEIMOS), the team actually confirmed that six galaxies are located around the black hole.
“We expect to discover further, fainter galaxies around this supermassive black hole. We may have just seen the tip of the iceberg" says co-author Felice Cusano, an astronomer at INAF in Bologna and observer for the LBT-Italy team.
These results contribute to our understanding of how supermassive black holes and large cosmic structures formed and evolved. The future ESO’s Extremely Large Telescope will be able to build on this research by observing higher numbers of fainter galaxies around massive black holes in the early Universe using its powerful spectroscopic instruments.
This research was presented in the paper “Web of the Giant: Spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524” to appear in Astronomy & Astrophysics.
The team is composed of M. Mignoli (INAF, Bologna, Italy), R. Gilli (INAF, Bologna, Italy), R. Decarli (INAF, Bologna, Italy), E. Vanzella (INAF, Bologna, Italy), B. Balmaverde (INAF, Pino Torinese, Italy), N. Cappelluti (Department of physics, University of Miami, Florida, USA), L. Cassarà (INAF, Milano, Italy), A. Comastri (INAF, Bologna, Italy), F. Cusano (INAF, Bologna, Italy), K. Iwasawa (ICCUB, Universitat de Barcelona & ICREA, Barcelona, Spain), S. Marchesi (INAF, Bologna, Italy), I. Prandoni (INAF, Istituto di Radioastronomia, Bologna, Italy), C. Vignali (Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Bologna, Italy & INAF, Bologna, Italy), F. Vito (Scuola Normale Superiore, Pisa, Italy), G. Zamorani (INAF, Bologna, Italy), M. Chiaberge (Space Telescope Science Institute, Maryland, USA), C. Norman (Space Telescope Science Institute & Johns Hopkins University, Maryland, USA).