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Detection of the Farthest Star by Hubble Space Telescope

This article appeared in the April 6, 2018 edition of the Davis Enterprise.

Detection of the Farthest Star by Hubble Space Telescope

Icarus, the farthest star. Photo by NASA.


By Vinita Domier

Special to the Enterprise


On April 2, 2018, an international team of astronomers announced that the Hubble Space Telescope had directly detected light from a star nicknamed Icarus that is the farthest star ever seen. This record-breaking observation of starlight that left Icarus around 9.4 billion years ago, a mere 4.4 billion years after the Big Bang, was possible due to the combined effects of gravitational lensing and microlensing that resulted from a rare and fortuitous cosmic alignment. Icarus is at least 100 times farther than any individual non-supernova star observed to date.


Gravitational lensing occurs when there is a massive distribution of matter between the light source and the observer like a galaxy cluster or supermassive blackhole. The diverging rays of light emanating from the source are bent due to the curvature in spacetime around the intervening matter distribution in direct proportion to its mass. This results in some of the source rays converging at the observer’s location producing a distorted image or images of the source depending on the massiveness of the foreground matter.


Gravitational microlensing occurs when there is a less massive and more discrete distribution of matter between the source of electromagnetic radiation and the observer like a star or a quasar. The diverging rays of radiation emanating from the source are slightly bent due to less warping of spacetime around the less massive intervening object. This results in some of the source rays converging at the observer’s location producing an undistorted single brighter image of the source but only when the foreground star/quasar is in alignment between the background source and the observer.


The gravitational lensing phenomenon was first predicted by Albert Einstein in 1915 in his Special Theory of Relativity. The first verification of this concept was achieved by Arthur Eddington during the 1919 total solar eclipse. He confirmed that the apparent location of background stars was measurably different from their true positions due to bending of starlight caused by the sun’s warping of spacetime around it.


In the case of the detection of Icarus, the foreground galaxy cluster, MACS J1149+2223, was 5 billion light years away in the Leo constellation. The combined lensing effects from this intervening supermassive cluster and a serendipitous alignment with a moving star in that cluster resulted in a 2000 times magnification of Icarus’ starlight.


Further spectral observations revealed that the star, officially known as MACS J1149+2223 Lensed Star 1, belongs in the blue supergiant family of main-sequence stars. As blue supergiants have lifespans of up to 10 million years, Icarus does not exist anymore. Also, even though blue giant stars are very luminous, without the combined magnification effects of gravitational lensing and microlensing, Icarus would have been undetectable by Hubble.


Join the Davis Astronomy Club on Saturday, April 7, starting at 7:30pm at the Explorit Science Center (3141 5th Street, Davis) when we will discuss gravitational lensing and its role in the historic detection of star Icarus. We will also briefly review Stephen Hawking’s immense contributions to cosmology and black holes. Everyone is invited to the free meeting indoors, followed by a star party outdoors (weather permitting).



Explorit’s coming events:


●      Summer Camp registration is open now! Visit for a full schedule and to register online. Or call 530-756-0191.

●      Visit our Feathers exhibition! Explorit’s Exploration Gallery is open to the public every Wednesday, Friday, Saturday and Sunday, 1:00-5:00 p.m.  Admission is $5.00 per person; Explorit members, teachers and children 2 and under are free.



Explorit Science Center is located at 3141 5th St. For more information call (530) 756-0191 or visit, or “like” us on Facebook at


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