A1 (marked here) is the brightest, hottest star in a young cluster called NGC 3603, in the southern Milky Way.

Credit: University of Montreal

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SYDNEY: Astronomers have unveiled both the biggest star and the most distant black hole ever found. These twin discoveries bring experts a few steps closer to unlocking the secrets of the early Universe.

Revealed last week at a meeting of the Canadian Astronomical Society in Kingston, Ontario, the finds easily exceed the previous record-holders and provide clues about the composition of the Universe soon after the Big Bang.

114 times our Sun

The new find, dubbed A1, is an astounding 114 times the mass of our Sun, which is already a hefty 1.988435×10³⁰ kg. This fiercely bright star is part of a binary system and sits at the centre of a giant, dense star cluster called NGC 3603, found 20,000 light years from Earth in the southern Milky Way. Its companion star has been weighed in at an impressive 84 solar masses.

The previous record-holder is the Pistol Star, 10 million times brighter than our Sun, yet weighing less than 100 solar masses – though even that find is contentious.

Physicists have estimated the biggest possible conventional star has a mass 150 times that of our Sun. Above that size, they say, the outward radiation pressure produced by nuclear fusion reactions would be greater than the star's gravity, rendering it dangerously unstable.

"What is important here is that this appears to be the most massive star that [has been] reliably measured," commented Michael Burton, an astrophysicist at the University of New South Wales in Sydney.

Data from the European Very Large Telescope and the Hubble Space Telescope allowed the masses of both stars in the A1 binary system to be measured simultaneously, by a research team at the University of Montreal who are behind the discovery.

Experts behind the find say that the holy grail of the star hunt would be detecting a massive, first generation star – literally, the 'mother of all stars', and this latest find is a step in the right direction.

First generation stars are among the first stars that formed and are made primarily from hydrogen and helium. They are predicted to measure up to several hundred solar masses; a possibility because of the lower radiation pressure due to smaller quantities of heavy elements in their core.

Ancient quasar

In a second ground-breaking discovery, an international team of astronomers, led by researchers at the University of Ottawa in Canada, have described the furthest known black hole.

Although black holes themselves are dark, they are capable of producing light. The black hole sucks in surrounding gas and dust, which heats up and glows with incredible intensity.

Quasars, which are believed to be young early galaxies with supermassive black holes at their core. They are the most luminous objects in the universe – some shine with a brightness more than a trillion times that of our Sun. More than 100,000 have been located to date.

The newly-found quasar, 1,000 times bigger than the one that may have formed our Milky Way galaxy, is named CFHQS J2329-0301, after the Canada-France High-z Quasar Survey, which uses a telescope in Hawaii in its search.

Redshift

The eight-metre-wide Gemini South telescope in Chile was also used to record the quasar's spectrum and associated redshift. The bigger the redshift seen in that spectrum, the further the object is from Earth, according to Hubble's law. A redshift greater than 6 places the object on the very limits of the visible universe, and means we're seeing something from billions of years ago. According to astronomers, the new quasar has a redshift of 6.43.

"As soon as I saw the spectrum ... I knew this one was a long way away," said Chris Willot, lead astronomer behind the discovery at the University of Ottawa. The light detected from this quasar has travelled for almost 13 billion years before it reaches Earth, he said.

The experts hope to use the find to confirm that the first stars and galaxies formed around a billion years after the Big Bang. And the find is already challenging existing theories.

"It's puzzling how such enormous black holes are found so early on in the history of the Universe," said team member John Hutchings, an astrophysicist at the Herzberg Institute of Astrophysics, Canada. "We believe black holes take a long time to grow."

Although astronomers are currently studying light from the quasar's early life, the quasar is unlikely to still be glowing and active.

"It will likely be sitting at the middle of a galaxy somewhere as a supermassive-black hole, gobbling the occasional star cluster now and then," comments Peter Tuthill, an astrophysicist from the University of Sydney.