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Skywatching

Space telescope spots 12.8 billion-year-old star

Spotting an ancient star

The image does not look very impressive, just a faint, somewhat blurry dot.

However, that dot is an image of the oldest and most distant individual star we have ever seen. Its light has taken 12.8 billion years to reach us.

Since the universe is around 13.7 billion years old, we are seeing a star that existed 900 million years after the beginning. Until this discovery, made using the Hubble Space Telescope (HST), the oldest individual star we had seen existed some four billion years after the beginning of the universe, so this discovery has taken us an enormous step back in time.

We have detected many galaxies as old, or possibly older than this recently discovered star, each of which contains billions of stars. However, those stars are so densely crowded together that even the HST cannot separate them into individuals. The resolution, or ability to discern fine detail, depends on the size of the lens or mirror making the image. To see a single star in such a remote galaxy would require an enormously larger lens. Fortuitously, in this case, one was available.

One of the predictions that came out of Einstein's work on relativity was the possibility of "gravitational lensing.” Massive objects bend light, focussing it to form an image, just as convex lenses do. There happens to be a large cluster of galaxies between us and that star, which act as a lens, increasing the magnification and resolution of the HST thousands-fold. Of course, a convenient gathering of galaxies won't be a perfect lens. However, this star falls in one of the better parts of the image, so we can actually see the star as an individual, rather than just a member of a dense crowd of billions, visible only as a glowing cloud.

The discoverers were fans of J.R.R Tolkien's writings and named the star Earendel —Dawn Star—after an elven mariner in the Silmarillion.

That long ago, the universe consisted almost completely of hydrogen and helium. All the other elements needed to make planets (and us) are the waste products from energy production by many generations of stars.

When Earendel formed, there were almost none of those other elements. The concentration of those waste products mixed in with the hydrogen and helium from which a star forms has a dramatic effect on the star.

Current theory suggests these stars were more massive than the stars we see around us now. However, even a small increase in mass dramatically increases the brightness of a star and the rate it consumes fuel. Earendel and his siblings had masses of possibly hundreds of times the mass of the Sun. The result is they shone incredibly brightly for maybe one or two million years, before running out of fuel, collapsing and exploding. Succeeding generations seeded the universe we see around us today with everything for making planets, people, and hopefully a bunch of aliens.

It is highly unlikely Earendel is the oldest star in the universe. With generations of hot, bright, massive stars passing at a rate of one every couple of million years, there could have been a few generations of earlier stars. This star was spotted because it was in the right place for a cluster of galaxies to gravitationally focus its light in the direction of the Hubble Space Telescope.

Looking for the oldest stars is not just record-seeking. The furthest back in time we can see is 380,000 years after the Big Bang, the era of the cosmic microwave background radiation. At that point the universe became totally dark, with great clouds of hydrogen and helium. Then, at some point the first stars formed, and there was light.

When did those first-ever stars form? What were they like? We have lots of ideas, but ideas are not facts. At what point in the history of the universe did planets and life become possible?

This is a big part of understanding our place in the universe, and just as important, whether we are alone.

•••

• Jupiter, Venus, Mars and Saturn are lined up low in the dawn glow. They are in order of increasing brightness.

• The Moon be full on April 16.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



More Skywatching articles

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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