Quasars & Other Supermassive Black Holes (SMBHs)

Quasars & Other Supermassive Black Holes (SMBHs)

Supermassive Black Holes (SMBH)

Supermassive Black Holes (SMBH) are NOT just large black holes, they are a different breed of beast. Both their size and rarity make this so. The Milky Way contains approximately 100 million black holes yet has ONLY ONE SMBH – Sagittarius A*. In fact, ALL GALAXIES contain only one SMBH ( unless two galaxies are merging when temporarily they will have more than one). Also the size differential between black holes and their Super massive counterparts is extreme. Ordinary black holes are typically 10- 100 solar masses, while SMBHs are MILLIONS TO BILLIONS of solar masses. Sagittarius A* is 4 million solar masses, while TON 618 one of the bigger SMBHs is 66 BILLION SOLAR MASSES!

Since all galaxies have one and only one, and the size of the SMBH is proportional to the size of the galaxy, obviously SMBHs are intimately linked to galaxy formation itself.

The Formation of Supermassive Black Holes

It is not clear yet how SMBHs form. It’s unlikely that they go through the normal sequence where a very large star runs out of fuel and collapses, SMBHs probably form from the direct collapse of Dark Matter clouds. This may occur since Dark Matter does not heat up when compressed so that density can increase to Black Hole density without ever getting hot enough to trigger nuclear fusion. Obviously, SMBHs will be critical in forming and subsequently sculpting all galaxies.

Quasars

ALL quasars are SMBHs, but not all SMBHs are quasars. Quasars are simply BRIGHT SMBHs. Let’s unpack that fact by describing the structure of an SMBH. Like all black holes, SMBHs are by definition black since they emit or reflect no light. This blackness is visible in pics we take as a dark shadow called the dark shadow! But like all black holes, SMBHs develop an accretion disk. The accretion disk is a matter that is being funneled into the black hole. As the matter spins in, it gets hotter and hotter such that near the event horizon it is traveling at near the speed of light. As it speeds up, via friction it heats up and emits light. Since the accretion disk has matter swirling around it at ALL TEMPERATURES it will emit a blackbody spectrum ( that light of every frequency) from radio waves to X-ray & gamma waves. The efficiency with whIch matter is converted to light is nearly 10%, far more efficient than a nuclear fusion of hydrogen to helium which operates at only 0.7 % efficiency. Additionally, since the SMBH and the plasma are spinning it creates a HUGE MAGNETIC PARTICLE ACCELERATOR which shoots half the ions& electrons & high energy photons (plasma) trying to accrete into the SMBH and SHOOTS them up in JETS at the poles perpendicular to the accretion disk. These jets shoot the plasma AT RELATIVISTIC SPEEDS (that means near the speed of light). Charged particles when accelerated give off SYNCHROTRON radiation, depending on the size of the particle anywhere from radio to X-ray in frequency, although MOST are IN THE RADIO. WAVELENGTH. Interaction of this plasma with high energy photons will even emit up to gamma rays (inverse Compton scattering)

Basically, a quasar is ANY SMBH that can devour enough matter via accretion to be very bright via the accretion disk and or jets.

Types of Quasars

This is actually very simple.

ALL SMBHs have the same structure-a central BH with Mass, Spin & Charge surrounded by a spinning accretion disk at its equator spiraling MATTER IN, and two jets at the poles spiraling MATTER OUT!

Even our own Sagittarius A* is of that configuration-BUT it’s not a quasar simply because there is not a lot of matter feeding into it. There was in the past as we see the remnant Fermi bubbles that were blasted out when Sagittarius A* was active in the past. Additionally, if it finds a new source of fuel may become active again.

Thus if you have a VERY LARGE SMBH, and you have A LOT of matter being devoured by the SMBH then it shines very very bright- ie a quasar! ( if an SMBH shines brightly at any wavelength- radio, visible or X-ray, etc. it’s known as an Active Galactic Nucleus- AGN)

If the accretion disk is obscured or quiescent and we primarily see the jets in radio waves we call it a radio galaxy. Same animal but at a different stage, or seen from a different angle.

Because quasars need a lot of ‘food’ to feed on to maintain their brightness they were far more abundant in the early universe. Thus the nearest quasar is over 66 million lightyears away.

Remember that quasars are so bright that the light they emit, from an area only solar system in size OUTSHINES the entire galaxy it’s embedded in.

Seifert galaxies are simply galaxies with medium power quasars, as bright but not brighter than the galaxy itself.

The biggest SMBHs result from mergers, thus elliptical galaxies which result from the merger of spiral galaxies will have huge mass SMBHs and lots of matter to feed on, and so are very bright quasars. If the radio emissions predominate they are termed radio galaxies.

The End Notes(What we see!)

Basically what you see depends on what wavelength you are measuring. In visible light, you will see the hot accretion disk wrapping around the SMBH at least triple the Schwarzschild radius and evidence of the jets extending megaparsecs perpendicular to the disk (1 megaparsec = 3.3 million lightyears) as the plasma interacts with the surrounding medium. The accretion disk to has a cloud of matter surrounding it called a torus that absorbs and then re-emits light producing an emission spectrum.

The lovely composite view of M87 an elliptical galaxy with the first SMBH actually visualized.