Interesting Facts About Quasars

More than 4 billion years into the future, when our Milky Way collides with the neighboring massive Andromeda galaxy, their central black holes will merge to form a supermassive black hole. It is most likely that this black hole will create a quasar, when it starts gobbling matter again.

Is it a star? Is it a galaxy? No, it is a quasar (quasi-stellar radio source).

With an energy output that is up to a 1,000 times more than our own Milky Way galaxy (which in itself is home to 200 to 400 billion stars) and an emission spectrum that stretches from infrared, visible, radio to gamma and X-ray sources, quasars have been the most puzzling objects to pin down for astronomers.

As light from the farthest reaches of the universe takes millions or billions of years to reach us, we are essentially looking at quasars as they were in the past.

In short, they are objects from the early universe, with the most phenomenal energy output, that is now believed to be powered by matter falling into a supermassive black hole (with a mass that is billions of times our Sun).

Collectively, they are now known to be a part of objects known as Active Galactic Nuclei (AGN). In this UniverSavvy article, we reveal some interesting factoids about these black hole-powered energy-spewing monsters, active in centers of young galaxies in the ancient universe.

From their source of energy being the gravitational action of supermassive black holes, to their phenomenal energy output over various electromagnetic wavelengths, every single fact about these objects is mind-boggling to say the least.

Quasars are compact regions at the very center of young galaxies, where gargantuan amounts of gas and dust are sucked in by the powerful gravitational pull of supermassive black holes.

According to current models, the infalling trapped matter is accelerated close to the speed of light (forming an accretion disc around the black hole), heating up due to friction in the process and emitting electromagnetic radiation in the infrared, visible, radio, and x-ray wavelengths through twin jets, pointed in opposite directions.

Though not even light can escape a black hole, matter and radiation can escape from outside the edges of its event horizon (the region around the black hole singularity that not even light can escape from). In short, a quasar is a black hole-powered dynamo, producing a phenomenal amount of radiation due to the friction of infalling matter.

These powerful energy sources were named as quasi-stellar objects as their electromagnetic radiation pattern in the visible and radio wavelengths, as well as their appearance as points of light in the sky, made them seem like stars initially.

Quasars are objects with a high redshift (their emission spectrum has values of increased wavelengths due to the Doppler effect, shifting them towards the red end of the spectrum), which indicates that these objects are receding very fast, away from us due to the very expansion of the spacetime fabric of our universe.

Considering Hubble's law (an object's receding speed is directly proportional to its distance from our galaxy), it can be inferred that these are distant objects in the universe, residing billions of light years away.

A consequence of the fact that these objects are radiating energy from billions of light years away, at the far edge of the known universe, is that we are looking at the distant past.

The light emitted by them is reaching us, billions of years later, providing us with a time machine of sorts, that looks into the past. This means quasars might be ancient objects, that probably powered galaxies in their infancy.

Through general-relativistic calculations, it has been estimated that the size of a quasar could be up to 10,000 times the Schwarzschild radius of the central supermassive black hole. Schwarzschild radius of a sphere is that length, within which, if the entire mass of the object is stuffed (compressed), its escape velocity would be equal to that of light.

Objects with a radius lesser than their Schwarzschild radius are black holes. Furthermore, through recent calculations, it has been estimated that most quasars will be limited to a size equal to the extent of our own solar system.

In terms of luminosity and energy output, quasi-stellar objects outshine our Milky Way, emitting thousands of times more energy, compared to our parent galaxy. It is primarily due to this high energy output, that they are seen even billions of light years away. The luminosity levels are known to be variable in most of them.

The exact mechanism that leads to the creation of relativistic jets in a quasar and other active galactic nuclei (AGNs), which may extend for several light years, is still unknown. When the jets are exactly directed towards our planet, the matter contained in them, appears to be traveling at speeds greater than light.

The Fermi Gamma-ray Space Telescope (FGST) has been launched to obtain observational evidence that could help understand the particle acceleration mechanics that drives these jets.

The monster black hole in an average quasar will gobble gas and dust worth 10 stars in a single year. The most luminous and powerful ones will gobble up to a 1,000 stars worth of matter in just about a year.

The first quasar, 3C48, was discovered by the American Astronomer Allan Sandage, in 1960, along with Thomas Matthews, using the technique of interferometry. Today, more than 200,000 quasars have been detected. Information about them can be obtained online, from the Sloan Digital Sky Survey.

The very first quasar to be discovered, which was also visible through an amateur telescope in the night sky, is 3C 273, located in the constellation Virgo (RA: 12^h 29^m 06.7^s; Dec: +02° 03′ 09″). With an apparent magnitude of 12.9, it is the brightest visible quasar in the sky.

It is located at a distance of 2.443 billion light years, with a redshift of 0.158. It is known to be radio-loud (high emission in the radio wavelengths of the electromagnetic spectrum) and was one of the first X-ray sources to be discovered outside our galaxy.

A very compact quasar, whose radiation jet is almost precisely pointed towards the Earth is known as a Blazar. 3C 273 is known to be such a blazar.

Discovered in 2011, ULAS J1120+0641 is a quasar found in the Leo constellation, with the highest known redshift (7.085±0.003), which puts its distance from Earth to be about 29 billion light years.

Its luminosity is estimated to be 6.3×10¹³ times Solar Luminosity (which is equal to 3.846 × 10²⁶ W), with a supermassive black hole powering it, that is estimated to be 2 billion times the Sun's mass. It will easily outshine an entire galaxy in terms of radiance and energy output.

Quasars have been detected in pairs and triplets (examples are LBQS 1429-008 and QQQ J1519+0627), being part of interacting galaxies which are gravitationally bound to each other.

Microquasars, a type of X-ray binary stars, are the miniature versions of massive quasars, powered by the energy emitted by infalling matter into a compact object like a neutron star or a black hole. The only difference being that the black holes or neutron stars aren't supermassive but smaller in comparison, comparable in mass to the Sun.

The infalling matter in their case, is derived from a companion star, and they display radio jets that are reminiscent of quasars. Some of the prime examples are Cygnus X-1, GRS 1915+105, and SS 433.

Quasars are a prominent type of active galactic nuclei. Depending on the angle of the relativistic jets of an AGN, with respect to our galaxy, we see them with different perspectives. If the jets are perpendicular and pointed away from us, they look like radio galaxies.

If the jet is pointed at an angle, with a substantial energy burst directed towards the Milky way, it is seen as a quasar. When the jet is precisely pointed towards us, what we see is a blazar.

When the monster black hole that creates the quasar has consumed all the matter around it, the energy creation engine comes to a halt and emission stops; becoming quiescent. Of course, this engine can start operating again, once enough matter comes in the proximity of the black hole again.

This is exactly what has happened with the massive black hole at the center our own Milky Way galaxy. In the future, a collision with Andromeda will trigger it back to life.

According to current cosmological models, the universe is infinite and expanding. To go by the likes of recent discoveries like quasars, it has just begun to unravel its magnificence and splendor and more mind-boggling revelations lay in store, in the future.

Blazars and active galactic nuclei remain intense subjects of research all over the world, as superior telescopes like the Chandra X-ray observatory and the Hubble Space Telescope are discovering newer objects at the very edge of the known universe.