Today’s Top Space Headline: The Supermassive Black Hole At the Dawn of the Cosmos –“Its Light the Most Distant Ever Detected”

 

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Since their discovery in 1963, astronomical objects called quasars have been among our most powerful probes of the early Universe. Initially seen as mysterious sources of extreme luminosity, quasars are now known to be supermassive black holes that are voraciously consuming gas from their immediate surroundings, emitting large amounts of radiation in the process.


In a paper in Nature, physicist Maximo Bañados and colleagues report observations of the most distant quasar found so far. The light detected from this object was emitted when the Universe was a mere 690 million years old — just 5% of its current age. With his first published article, “The Black Hole in Three-Dimensional Space-Time,” Bañados established himself as an innovative, insightful physicist.

 

Bañados' quasar, known as ULAS J1342+0928, has a redshift of 7.54,  reports the journal Nature. This means that its strong ultraviolet emission has been shifted into the near-infrared, beyond the sensitivity of typical imaging surveys of the sky. Finding such a high-redshift quasar was not possible until about a decade ago, when sufficiently sensitive near-infrared detectors began scanning large areas of the sky.

The image below shows th emission from a quasar, extremely luminous astronomical objects that comprise a supermassive black hole surrounded by an orbiting disk of gas called an accretion disk. As material in the disk is pulled towards the black hole, energy is released in the form of electromagnetic radiation and, in some cases, as beams of charged particles called jets.

 

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By studying the absorption spectrum of ULAS J1342+0928 (the fraction of incident radiation absorbed by the intergalactic medium over a range of frequencies), the authors determined that the neutral proportion of hydrogen was at least 10% when the Universe was 690 million years old, which sets a strong constraint on how the intergalactic medium was reionized.

The quasar’s black hole is extremely massive — about 800 million times the mass of the Sun. Black holes grow by consuming (accreting) gas from a surrounding structure called an accretion disk (Fig. 1). The gas emits radiation as it falls in. However, such systems have a maximum luminosity, which occurs when the pressure of the emitted light pushes away the infalling gas, halting further growth. This luminosity depends on the mass of the accreting black hole, and therefore defines a maximum growth rate, known as the Eddington limit, for the system.

Bañados suggests that the large mass of the black hole in ULAS J1342+0928 can be explained if the object began its life as an initial (seed) black hole of at least 1,000 solar masses. This result could rule out models in which black-hole seeds were created from the deaths of the first massive stars, and instead favour models in which these seeds formed from the direct collapse of primordial gas.

In addition, the black hole would need to have grown continuously (and, therefore, exponentially) at the Eddington limit, starting from when the Universe was roughly 65 million years old. Although this scenario is physically possible, it requires extreme, sustained accretion for about 600 million years, which is substantially longer than the typical lifetime of a quasar.

So far, only two quasars with redshifts greater than 7 have been discovered. The previous record holder was reported in 2011, and early models of quasar evolution predicted that more should have been found by now11. The methods for finding quasars, even at these high redshifts, are sound and have been proved effective. The dearth of high-redshift quasars might indicate that these objects were uncommon in the early Universe, and could imply a sharp decline in quasar activity towards early times.

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Image credit:  With thanks to J Wise, GA Tech and J Regan Dublin City

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