Confirmed: Black holes regulate star formation in massive galaxies

January 31, 2018

The centres of massive galaxies are among the most exotic regions in the universe. They harbour supermassive black hole, with masses of at least one million, and reaching thousands of millions of times the mass of the Sun. These black holes can cause a great deal of matter to fall towards them, producing the emission of huge quantities of energy before they finally fall into the black hole. In addition during this period (the "active phase" of the galaxy, referred to as an AGN or Active Galactic Nucleus) matter is expelled from outside the black hole in the form of high velocity (relativistic) jets, which can produce violent shocks with the surrounding matter.

For some time it has been thought that all of this emission of radiation and particles, and the growth of the black hole itself, should influence the way in which these galaxies form stars, making this star formation more difficult. "This influence " explains the first author of the article, Ignacio Martín Navarro, who studied for his doctorate at the Instituto de Astrofísica de Canarias (IAC) and the Universidad de La Laguna (ULL) and who is at present a researcher at the University of California at Santa Cruz (US) and the Max Planck Institut für Astronomie (Heidelberg, Germany), "allows us to explain the observed relations such as that between the mass of the central black hole and the total stellar mass. In fact without this "feedback" the simulations of the formation and the evolution of massive galaxies fail completely, both in reproducing their properties and in the number of galaxies predicted with a given mass". However until now there has been no observational evidence in favour of this idea which has become increasingly well known and established.

"In this work", adds Ignacio, "we analyse the spectra of the centres of 74 galaxies using data from the Hobby-Eberly Telescope Massive Galaxy Survey with the aim of finding out how the rate of star formation in these systems ahs changed during their lifetimes (the "star formation history"). To do this we used codes which allow us to compare the observed spectra with those predicted by models of stellar evolution. In this way we can learn how many stars of different ages there are in each of the observed galaxies".

"As a result of this analysis", explains Tomás Ruiz Lara, a researcher at the IAC and one of the authors of the Nature article, "we can explore the different star formation histories in galaxies with black holes of different masses. Our findings suggest clearly that, in effect, supermassive central black holes can affect the formation of stars throughout the lifetime of the galaxy, and that this effect depends on their masses".

According to this analysis, galaxies with more massive black holes in their centres show a faster rate of initial star formation, which gives rise to a more massive back hole which then can slow down the star formation in the galaxy. On the contrary, this process is produced much more slowly in those stars which currently harbour less massive black holes, starting with a lower star formation efficiency. " To be specific", stresses Ruiz Lara, "we find that the galaxies with the most massive central back holes form the major part of their masses (95%) up to 4,000 million years before the galaxies with less massive central black holes. But at the same time, the more recent star formation (during the last 700 million years) is greater for galaxies with less massive black holes".

The fact that the mass of these black holes is related to the quantity of matter and energy emitted during their AGN phase (which was well known), taken together with the new results, confirm a simple scenario previously envisaged, which has been clearly strengthened thanks to this study. To form stars efficiently, cold gas and dust are needed. However the energy and the particles emitted from the centre of a galaxy during its AGN phase can heat the interstellar medium through which they pass, reducing the possibility of star formation. For higher emission (which implies for greater mass of the central black hole), lower will be the efficiency of the host galaxy in forming its stars. This gives a ready explanation of why galaxies with the most massive black holes suppress their initial star formation first, so that more recent star formation is not favoured.

These results published in Nature which have a key importance in modern astrophysics and have been sought with great intensity during the past 20 years, offer key observational evidence for widely accepted hypotheses which are basic for understanding how the most massive galaxies form and evolve.
Paper: Ignacio Martín-Navarro et al. "Black-hole regulated star formation in massive galaxies", Nature. doi:10.1038/nature24999

Instituto de Astrofísica de Canarias (IAC)

Related Black Hole Articles from Brightsurf:

Black hole or no black hole: On the outcome of neutron star collisions
A new study lead by GSI scientists and international colleagues investigates black-hole formation in neutron star mergers.

The black hole always chirps twice: New clues deciphering the shape of black holes
A team of gravitational-wave scientists led by the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) reveal that when two black holes collide and merge, the remnant black hole 'chirps' not once, but multiple times, emitting gravitational waves--intense ripples in the fabric space and time--that inform us about its shape.

Wobbling shadow of the M87 black hole
New analysis from the Event Horizon Telescope (EHT) Collaboration reveals the behavior of the supermassive black hole in the center of the M87 galaxy across multiple years, indicating the crescent-like shadow feature appears to be wobbling.

How to have a blast like a black hole
Scientists at Osaka University have created magnetized-plasma conditions similar to those near a black hole using very intense laser pulses.

Black hole collision may have exploded with light
Astronomers have seen what appears to the first light ever detected from a black hole merger.

Black hole's heart still beating
The first confirmed heartbeat of a supermassive black hole is still going strong more than ten years after first being observed.

Black hole team discovers path to razor-sharp black hole images
A team of researchers have published new calculations that predict a striking and intricate substructure within black hole images from extreme gravitational light bending.

Planets around a black hole?
Theoreticians in two different fields defied the common knowledge that planets orbit stars like the Sun.

Black hole mergers: Cooking with gas
Gravitational wave detectors are finding black hole mergers in the universe at the rate of one per week.

Going against the flow around a supermassive black hole
At the center of a galaxy called NGC 1068, a supermassive black hole hides within a thick doughnut-shaped cloud of dust and gas.

Read More: Black Hole News and Black Hole Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to