Supermassive black holes can shut down star formation during cosmic noon:
- Outflows The most powerful Active Galactic Nuclei (AGN) can drive massive outflows that can remove all of the gas from their host galaxies in a relatively short amount of time. These winds can potentially push gas out of galaxies, causing galactic “outflows”.
- Star production Galaxies with lots of gas and dust in their central region are ripe for star production. However, they are also the perfect setting for supermassive black holes to grow larger.
- Feedback The feedback from supermassive black holes regulates star formation throughout the entire galaxy. Without outflows from giant black holes, star formation would happen much faster.
The interplay of supermassive black holes and their host galaxies is one of the key unsolved questions in astronomy.
According to this consensus, an AGN’s powerful radiation will expel cold gas while heating the gas reservoir in the galactic halo. This prevents said gas, which fuels star formation, from cooling and being re-accreted to replenish the reservoir.
Supermassive black holes can control star formation in galaxies in a few ways:
- Quenching Black holes can encourage quenching, which is the process by which galaxies stop star formation. They can do this by heating up stellar material and preventing it from condensing into new stars.
- Blowing away gas and dust The energy of supermassive black holes can blow gas and dust away.
- AGN feedback During growth, black holes release large amounts of energy across the electromagnetic spectrum. This energy is believed to regulate the rate of star formation in the black holes’ host galaxies.
- Clearing large areas Black holes may clear large bubble-like areas in the outskirts of their host galaxies. When small satellite galaxies travel through these areas, they will form more stars than they otherwise would.
- Eject plasma jets When particles that were infalling onto these black holes are trapped by magnetic fields, they can be ejected outwards and travel far inside galaxies in the form of enormous and powerful jets of plasma. These jets are often perpendicular to galactic disks.
Some observational evidence that supermassive black holes are located at the centers of many galaxies includes:
- Star movement Stars near the galactic center move as though they are influenced by the immense gravitational pull of a supermassive black hole
- Powerful jets Powerful jets of matter and energy emanating from the centers of galaxies are thought to be produced by supermassive black holes as they consume surrounding matter
- Doppler effect Light from nearby orbiting matter is red-shifted when receding and blue-shifted when advancing
- Space distortion The black hole distorts the space around it, which warps images of stars lined up almost directly behind it
Other evidence includes:
- Optical and radio observations which show a sharp rise in the velocities of stars or gas clouds orbiting the centers of galaxies
- The entire Milky Way galaxy is observed to be rotating around a black hole that has a mass about 4.6 million times greater than that of our sun
- A plot of the orbital motion of the star S2 around the centre of the Milky Way
It’s possible that some very small galaxies, such as dwarf galaxies, may not have black holes due to their size and lack of sufficient mass to form one. There are also galaxies that don’t have a central black hole, such as the Triangulum galaxy. Disk galaxies without a central bulge of stars, like the neighboring galaxy Messier 33, either have no black hole or have only tiny black holes that are well below Hubble’s detection limit.
Galaxies form out of immense clouds of gas that collapse and rotate. As they evolve, stars form within them.
The Triangulum Galaxy, also known as M33, is a galaxy that does not appear to have a supermassive black hole at its center. However, it does have a black hole named M33 X-7, which is the largest stellar mass black hole known. M33 X-7 orbits a companion star that it eclipses every 3.5 days.
Other galaxies that don’t have a central black hole include:
- Irregular galaxies These galaxies don’t have a bulge, which makes them stand apart from their galactic counterparts.
- A2261-BCG This massive galaxy has a bulge, but the central stellar velocity dispersion is low, implying there is no black hole at its core.
Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies, even our own Milky Way. However, only a minuscule fraction of dwarf galaxies is known to host intermediate-mass black holes.
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