by A new study published in Nature Astronomy describes the most luminous object astronomers have ever seen. It is a black hole with the mass of 17 billion Suns, swallowing more mass than the Sun every single day.
It has been known for many years, but since it is so bright, astronomers assumed it must be a nearby star. Only recent observations have revealed its length and brightness.
The object is called J0529-4351. This name simply refers to its coordinates on the celestial sphere – a way of projecting the objects in the sky onto the inside of a sphere. It is a type of object called a quasar.
The physical nature of quasars was initially unknown. But in 1963, the visible light from a quasar called 3C 273 was split into all its wavelengths (called its spectrum). This indicated that it was located almost 2 billion light years away.
Given how bright 3C 273 is to us, and how far away it is from us, it must be extremely luminous – a term in astronomy that refers to the amount of light an object emits in a unit of time. The only known source of power for such extreme luminosity was matter that fell into a supermassive black hole. So quasars are the most actively growing black holes in the universe.
Power source
Supermassive black holes often sit at the center of galaxies. Like all quasars, J0529-4351 is powered by material, mostly superheated hydrogen and helium gas, falling into its black hole from the surrounding galaxy.
About once the mass of the Sun is falling into this black hole every day. A question in astrophysics is exactly how so much gas can be injected into the center of galaxies to increase the mass of black holes.
In the center of the galaxy, the gas forms in the shape of a thin disk. The properties of viscosity (resistance to the flow of matter in space) and friction in the thin disk help heat the gas to thousands of degrees Celsius. This is hot enough to glow when viewed at visible and ultraviolet light wavelengths. It is that glow that we can see from Earth.
At about 17 billion Suns in mass, J0529-4351 is not the largest known black hole. One object, in the center of the galaxy cluster Abell 1201, is equivalent to 30 billion Suns. However, we must remember that because of the time it takes for light to travel across the great distance between this object and Earth, we are looking at it when the universe was only 1.5 billion years old . It is now about 13.7 billion years old.
So this black hole must have been growing, or accreting, at this rate for a significant fraction of the age of the universe by the time it was observed. The authors believe that the accretion of gas from the black hole is occurring close to the limit set by the laws of physics. Faster accretion creates a more luminous disk of gas around the black hole that can stop any further infalling matter.
The story of discovery
J0529-4351 has been known for many years, but despite having a gas accretion disk 15,000 times the size of our Solar System and occupying its own galaxy – probably close to the size of the Milky Way – it is so far from it appears as a single point of light in our telescopes.
This means that it is difficult to distinguish from the billions of stars in our own galaxy. To discover that it was, in fact, a superpowerful black hole far away, required more complex techniques. First, astronomers collected light from the middle of the infrared waveband (light with wavelengths much longer than those we can see).
Stars and quasars look very different from each other at those wavelengths. To confirm the observation, a spectrum was taken (as with the quasar 3C 273), using the Australian National University’s 2.3 meter telescope at Siding Spring Observatory, New South Wales.
And, as with 3C 273, the spectrum revealed the nature of the object and how far away it was – 12 billion light years. This showed how great her insanity must have been.
Detailed checks
Despite these measurements, several checks needed to be made to confirm the true brightness of the quasar. First, astronomers had to make sure that the light was not amplified by a source in the sky that was closer to Earth. Like lenses used in glasses or binoculars, galaxies can act as lenses. They are so dense that they can bend and amplify light from more distant sources perfectly aligned behind them.
Data from the European Space Agency’s Gaia satellite, which has extremely precise measurements of J0529-4351’s position, was used to determine that J0529-4351 is a single unlensed light source in the sky. This is supported by more detailed spectra taken with the European Southern Observatory’s Very Large Telescope (VLT) facility in Chile.
J0529-4351 is likely to be a very significant tool for studying quasars and black hole growth in the future. The mass of black holes is a fundamental property but very difficult to measure directly, as there is no standard set of weighting scales for absurdly large mysterious objects.
One technique is to measure the effect of the black hole on more diffuse gas orbiting in large clouds, known as the “broad line region”. This gas is revealed in the spectrum by broad “emission lines”, which are caused by electrons jumping between specific energy levels in the ionized gas.
The width of these lines is directly related to the mass of the black hole, but the calibration of this relationship is tested very poorly for the most luminous objects such as J0529-4351. However, because it is so physically large and so luminous, J0529-4351 will be visible by installing a new instrument on the VLT, called Gravity+.
This instrument will provide a direct measurement of the black hole’s mass and calibrate the relationships used to estimate masses in other high-luminosity objects.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Philip Wiseman works at the University of Southampton and is funded by the Science and Technology Facilities Council.
