Last updated April 9, 2018 at 11:54 am
Astronomers have discovered the furthest star ever seen, over 9 billion light years away from Earth.
Icarus, whose official name is MACS J1149+2223 Lensed Star 1, is the farthest individual star ever seen. It is only visible because it is being magnified by the gravity of a massive galaxy cluster, located about 5 billion light-years from Earth. Called MACS J1149+2223, this cluster, shown at left, sits between Earth and the galaxy that contains the distant star. The panels at the right show the view in 2011, without Icarus visible, compared with the star’s brightening in 2016.
Credit: NASA, ESA, and P. Kelly (University of Minnesota)
What might seem like a tiny speck amongst a vista of galaxies might be one of the most remarkable photos ever taken.
According to NASA the tiny pinprick of light, too faint to view even with the world’s largest telescopes, is the furthest star ever seen.
Captured by the Hubble Space Telescope, the enormous blue star is around 9 billion light years away – more than half of the distance across the universe.
“This star is at least 100 times farther away than the next individual star we can study, except for supernova explosions,” said Dr Patrick Kelly from the University of Minnesota, who lead the research.
Nicknamed Icarus but officially named MACS J1149+2223 Lensed Star 1, it would have by now died, most likely forming a neutron star or black hole.
The cosmic quirk which allowed discovery
The discovery of Icarus was possible due to a quirk of the universe – an effect called gravitational lensing.
Gravity from a massive cluster of galaxies between Icarus and Earth acted as a natural lens in space, bending and amplifying light. This means that sometimes light from a single background object can appear as multiple images, but the light can be highly magnified, making extremely faint and distant objects bright enough to see.
Without it, the feeble light of Icarus would have been too dim to detect, even for a telescope like Hubble.
The galaxy causing the lensing in this case was a galaxy cluster called MACS J1149+2223, located about 5 billion light-years from Earth and positioned between us and the galaxy that contains the distant star.
Usually MACS J1149+2223 amplifies the light from Icarus by around 600 times. However, a change in the galaxy – possibly a star moving in front of Icarus – meant the light momentarily skyrocketed to 2,000 times its true brightness when it received a temporary boost in magnification.
Characterizing Icarus
The international team of astronomers had been using Hubble to monitor a supernova in the far-distant spiral galaxy when they spotted a new point of light not far from the magnified supernova.
Its position suggested that the light was being much more highly magnified than the supernova.
When they analysed the colours of the light coming from this object, they discovered it was a blue supergiant star. This type of star is much larger, more massive, and possibly hundreds of thousands of times intrinsically brighter than our Sun.
It is also thought to be far hotter, with surface temperatures between 11 000 and 14 000 degrees Celsius.
But at this distance, it would still be too far away to see without the boosted amplification of the gravitational lensing.
“The source isn’t getting hotter; it’s not exploding. The light is just being magnified,” said Kelly. “And that’s what you expect from gravitational lensing.”
This image shows the the huge galaxy cluster MACS J1149.5+223, whose light has taken over 5 billion years to reach us. Highlighted is the position where the star LS1 appeared — its image magnified by a factor 2000 by gravitational microlensing. The galaxy in which the star is located can be seen three times on the sky — multiplied by strong gravitational lensing. Credit: NASA, ESA, S. Rodney and the FrontierSN team
Probing for dark matter
The discovery of Icarus has now provided a new opportunity for the astronomers to investigate dark matter, by probing the galaxy cluster causing the lensing.
By examining the bending and amplification of the light, and the event that caused the temporary boost in magnification, the team could detect neutron stars and black holes, which are otherwise invisible and they can estimate how many of these dark objects exist within this galaxy cluster.
One theory of dark matter is that it might be made up mostly of a huge number of primordial black holes formed in the birth of the universe with masses tens of times larger than the Sun.
However, the results from Icarus don’t support that hypothesis. According to the researchers, fluctuations in the light from the background star, monitored with Hubble for 13 years, would have looked different if there were a swarm of intervening black holes.
“If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1,” said Kelly.
“Our observations do not favour the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun.”
With the future launch of the James Webb Space Telescope (recently delayed again until 2020), astronomers are hoping that the discovery of more stars like Icarus may become more routine. Webb’s extraordinary sensitivity will allow measurement of even more details of these incredibly distant and old objects, and that may make it possible to study the evolution of the earliest stars in the Universe in greater detail than ever expected.
The research has been published in Nature Astronomy
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