SLOW-MO SUPERNOVA
Mystery of the star that wouldn’t die
POINTY OBJECT FROM AFAR
An asteroid discovered about 20 million miles away on 19 October, known as ‘Oumuamua, is one of the most elongated cosmic objects known to science. Its speed and trajectory strongly suggest it originated in a planetary system outside our own. Astronomers scrambled to observe the unique rock before it fades from view. It appears to be at least 10 times longer than it is wide, a ratio more extreme than that of any asteroid or comet ever observed in our Solar System. There is nothing natural that comes close to it in shape and no process of nature we know of that could have shaped it, though one suggestion is that it was shot away from its home star by a supernova explosion. Scientists from the Breakthrough Listen project, which searches for evidence of alien civilisations, monitored the rock on four different radio transmission bands. “Most likely it is of natural origin, but because it is so peculiar, we would like to check if it has any sign of artificial origin, such as radio emissions,” said Avi Loeb, professor of astronomy at Harvard.
Using observations from the Very Large Telescope in Chile, Karen Meech, from the Institute for Astronomy in Honolulu, Hawaii, and colleagues determined that ‘Oumuamua was about 400m (1,312ft) long – slightly shorter than the Empire State Building – rapidly rotating, brightening and dimming dramatically every 7.3 hours, giving a clue to its bizarre shape. “One has to realise we don’t know where the rotation pole is pointed,” said Dr Meech. “We assumed that it was perpendicular to the line of sight. If it were tipped over at all, then there are projection effects and the 10:1 is a minimum. It could be more elongated!”
‘Oumuamua – pronounced oh-MOO-a-MOO-a – means “a scout or messenger from afar arriving first” in Hawaiian. It has a reddish colour, similar to objects in the outer Solar System, and is completely inert, without the faintest hint of dust around it. These properties suggest that ‘Oumuamua is dense, comprising rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over long periods of time. Although it formed around another star, scientists think it could have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our Solar System. It appears to have come from the general direction of where the Vega star system is now (25 light years away in the northern constellation of Lyra), which should make any space nerd squeal with glee as Vega featured in the novel and movie
Contact. Unfortunately, it wasn’t actually in that part of the sky when the asteroid was there 300,000 years ago, according to the European Southern Observatory.
The cosmic interloper was discovered by Rob Weryk, a postdoctoral researcher at the Institute for Astronomy and a co-author of the new study, which is published in Nature. Weryk realised it was going fast enough to avoid being captured by the Sun’s gravitational pull, and was on a very eccentric trajectory taking it out of our Solar System, bound for the Pegasus constellation. It reached a peak speed of 196,000mph (315,500km/h) as it swept past the Sun. By next May it will be passing Jupiter. Guardian, 28 Oct, 11 Dec; BBC News, mashable.com, 20 Nov; D.Mail, 22 Nov; NY Times, 24 Nov 2017.
GOLD IN VAST QUANTITIES
Gold forged from the titanic collision of two super-dense stars has made an alchemist’s dream came true 130 million light years from Earth. Enough gold to match the mass of 200 Earths was created in the nuclear furnace lit by merging neutron stars in a galaxy called NGC 4993. It also created huge quantities of platinum and uranium and other heavy elements such as lead. The spectacular event was recorded by astronomers in the US on 17 August 2017 and generated ripples in the fabric of the Universe, leading to the fifth detection of gravitational waves on Earth. (The first discovery of such waves was in September 2015, confirming a prediction made by Einstein a century ago and earning Nobel Prizes for Rainer Weiss, Kip Thorne and Barry Barish.) Scientists not only ‘heard’ the collision by measuring vibrations in spacetime, but also used satellite and ground-based telescopes to see light and radiation pouring out of the stellar fireball, dubbed a ‘kilonova’.
Every other gravitational wave detection has been traced to black holes crashing together in remote regions of the Universe more than a billion light years away. The new event – though still very distant – was much closer and completely different in nature. It was caused by colliding neutron stars – burnt out remnants of giant stars so dense that a teaspoon of their material on Earth would weigh a billion tons. The two objects, each about 12 miles (19km) in diameter, stretched and distorted space-time as they spiralled towards each other and finally collided. The discovery also solved the mystery of what creates short-wave gamma ray bursts picked up on Earth, and could help pinpoint how fast the Universe is expanding. NY Times, 4 Oct; <i> D.Telegraph, D.Mail, Guardian, 17 Oct 2017.