The Hubble Telescope has just spotted the most distant star ever detected

The Hubble Space Telescope observed the most distant star ever seen – Earendel, which means morning star. Even though Earendel is 50 times the mass of the Sun and millions of times brighter, we wouldn’t normally be able to see it. We can see this due to an alignment of the star with a large cluster of galaxies in front of it whose gravity bends the light from the star to make it brighter and more focused – essentially creating a lens.

Astronomers see into the distant past when we look at distant objects. Light travels at a constant speed (3×10⁸ meters per second) so the further away an object is, the longer it takes for the light to reach us. By the time light reaches us from very distant stars, the light we observe may be billions of years old. So we are looking at events that happened in the past.

When we observe starlight, we are looking at light that was emitted from the star 12.9 billion years ago – we call this the lookback time. It’s just 900 million years after the Big Bang. But because the universe also expanded rapidly during the time it took for that light to reach us, Earendel is now 28 billion light-years away from us.

Now that Hubble’s successor, the James Webb Space Telescope (JWST), is in place, it may be able to detect even older stars, although there may not be many that are well aligned. to form a “gravitational lens” so we can see it. .

To see further in time, objects must be very bright. And the most distant objects we have seen are the most massive and brightest galaxies. The brightest galaxies are those containing quasars – luminous objects thought to be powered by supermassive black holes.

Prior to 1998, the most distant detected quasar galaxies were approximately 12.6 billion years of retrospection time. Improved resolution from the Hubble Space Telescope has increased the lookback time to 13.4 billion years, and with the JWST we plan to improve it to 13.55 billion years for galaxies and stars.

Stars began to form a few hundred million years after the Big Bang, at a time we call the cosmic dawn. We would like to be able to see the stars at cosmic dawn, because it could confirm our theories about the formation of the universe and galaxies. That said, research suggests that we may never be able to see the most distant objects with telescopes in as much detail as we would like – the universe may have a fundamental resolution limit.

Why look back?

One of JWST’s main goals is to find out what the early universe looked like and when the first stars and galaxies formed, between 100 and 250 million years after the Big Bang. And, luckily, we can get clues about it by looking even deeper than Hubble or the JWST can handle.

We can see light from 13.8 billion years ago, although it’s not starlight – there were no stars then. The farthest light we can see is the Cosmic Microwave Background (CMB), which is the residual light from the Big Bang, which formed just 380,000 years after our cosmic birth.

The universe before the formation of the CMB contained charged particles of positive protons (which now make up the atomic nucleus with neutrons) and negative electrons, as well as light. The light was scattered by the charged particles, which made the universe a misty soup. As the universe expanded, it cooled until electrons combined with protons to form atoms.

Unlike the soup of particles, atoms had no charge, so light was no longer scattered and could travel through the universe in a straight line. This light continued to travel through the universe until it reached us today. The wavelength of light has lengthened as the universe has expanded – and we currently see it as microwaves. This light is the CMB and can be seen uniformly from all points in the sky. The CMB is everywhere in the universe.