The Hubble Space Telescope has been used to observe the most distant star ever found. The star, called Lensed Star 1 (LS1), existed just 4.4 billion years after the Big Bang, and its light was emitted when the Universe was about 30 per cent its current age, but this light has only just reached us.
It was found using a technique called ‘gravitational lensing’ that works on the basis that mass warps space-time.
This means that the light from distant objects in space is magnified by the mass of huge objects that are closer.
This enables astronomers to observe objects that would otherwise be too far away to see.
Astronomers were using Hubble to detect a supernova called ‘Refsdal’ in the galaxy cluster MACS J1149-2223, when they spotted the star unexpectedly.
The star’s light was magnified about 2,000 times by the total mass of the galaxy cluster, but also by an object about three times the mass of our Sun that exists within the cluster.
Further Hubble observations revealed that the star is a B-type supergiant.
These are extremely luminous and blue in colour, and have a surface temperature between 11,000 and 14,000°C; more than twice as hot as the Sun.
“The discovery of LS1 allows us to gather new insights into the constituents of the galaxy cluster,” says Steven Rodney of the University of South Carolina, a member of the team that made the discovery.
“We know that the microlensing was caused by either a star, a neutron star, or a stellar-mass black hole.”
This image shows a section of the galaxy cluster in which the star was discovered. Circled in red is the position where the star appeared. Credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the FrontierSN team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)
This revelation means that LS1 can enable astronomers to learn more about neutron stars and black holes, which are otherwise invisible.
It could also reveal more about the elusive substance known as dark matter.
“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,” says Patrick Kelly of the University of Minnesota, who led the study.