Graham writes ... The real identity of what was thought to be a rather uninteresting nearby star was revealed in an article in Nature Astronomy on 19 February. The star, which is labelled J0529-4351, was first catalogued in a Southern Sky Survey dating back to 1980 (the rather uninteresting name is derived from the object’s celestial coordinates). Also, more recently, automated analysis by ESA’s Gaia spacecraft catalogued it as a star. The lead author of the article in Nature, Christian Wolf, is based at the Australian National University (ANU), and it was his team that first recognised the star’s true identity as a quasar last year, using the ANU’s 2.3 metre telescope at Siding Springs Observatory. As an aside, there is a relatively local link with this telescope, as it was once housed at Herstmonceux, Sussex as part of the Royal Greenwich Observatory. The true nature of the ‘star’ was further confirmed using the European Southern Observatory’s Very Large Telescope in Northern Chile. You can see the ANU’s press release here. So, what’s a quasar you might ask? A quasar (standing for ‘quasi-stellar object’) is an extremely luminous active galactic nucleus. When first discovered in the 1960s, these star-like objects were known by their red-shift to be very distant from Earth, which meant that they were very energetic and extremely compact emitters of electromagnetic radiation. At that time, the nature of such an object with these characteristics was a subject for speculation. However, over time, we have discovered that super-massive black holes at the centre of galaxies are ubiquitous throughout the Universe. Indeed, we have one at the centre of our own Milky Way galaxy with a mass of 4 million Suns, just 27,000 light years away. So, when we observe a quasar, the light has taken billions of years to reach us, and we are seeing them as they were in the early Universe when galaxies were forming. In those early structures, ample gas and matter debris was available to feed the forming black holes, creating compact objects with a prodigious energy output. And this is what J0529-4351 turned out to be. This object’s distance was estimated to be 12 billion light years (a red-shift of z = 4), with a mass of approximately 17 billion Suns, hence dwarfing our Milky Way black hole. As black holes feed on the surrounding available material (gas, dust, stars, etc.) they form an encircling accretion disk, in which the debris whirlpools into the centre. Velocities of material objects in this disk approach that of light speed, and the emission from the quasar radiates principally from this spiralling disk. The accretion disk of J0529-4351 is roughly 7 light years in diameter, with the central blackhole consuming just over one solar mass per day. This gives the object an intrinsic brightness of around 500 trillion Suns, making it the brightest known object in the Universe. Hopefully, like me, you are awed at the characteristics of this monstrous black hole that provided this amazing light show 12 billion years ago! Apologies that this month’s blog is shorter than usual, mainly because of preparation work required for next month’s conference at Lee Abbey, Devon, UK (see information on the home page). For those booked in, we are really looking forward to meeting you all next month!
John has also been busy posting other item(s) of interest on our ‘Big Bang to Biology’ Facebook page. Graham Swinerd Southampton, UK February 2024
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