Dust-rich early galaxy discovered

A distant galaxy whose light is only just reaching Earth is providing astronomers with a glimpse into the early Universe.

A view of galaxy cluster Abell 2744 by the Hubble Space Telescope. Beyond this cluster, seen inset, is galaxy A2744_YD4. The galaxy is so far away, astronomers could only view it using a technique called gravitational lensing, in which closer, massive galaxies act as a sort of cosmic telescope.
Credit: ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO and D. Coe (STScI)/J. Merten (Heidelberg/Bologna)


A distant galaxy has been discovered that is providing astronomers with a look at the early Universe, and revealing clues as to when the first stars shone light across the cosmos.

ESO’s ALMA telescope was used to view the galaxy, which is so far away its light has only relatively recently reached Earth. It appears to astronomers as it did when the Universe was just 600 million years old and the first stars began forming.

This makes A2744_YD4 the youngest and most remote galaxy ever seen by the ALMA telescope; a fantastic opportunity to study how galaxies and stars looked when our Universe was in its infancy.


Read more on this subject from BBC Sky at Night Magazine


Observations revealed the galaxy contains cosmic dust, which is formed during the explosive deaths of earlier generations of stars, revealing that this galaxy must have experienced some of the first supernova explosions in the history of the Universe. This dust contains mostly silicon, carbon and aluminium, which are ingredients vital for new stars to form. While in today’s Universe this dust is in abundance, it was scarce in the early Universe, meaning astronomers are getting closer to pinpointing the period during which the first hot stars shone light. Despite this relative scarcity, estimates suggest the amount of dust in the galaxy is equal to six million times the mass of our Sun.

Observations also revealed glowing ionised oxygen coming from the galaxy; the earliest detection of oxygen in the Universe. 

The team behind the study measured the rate of star formation in A2744_YD4 and found that stars are forming at a rate of 20 solar masses per year, compared to one solar mass per year in the Milky Way.

“This rate is not unusual for such a distant galaxy, but it does shed light on how quickly the dust in A2744_YD4 formed,” says ESO’s Richard Ellis, a co-author of the study. “Remarkably, the required time is only about 200 million years — so we are witnessing this galaxy shortly after its formation.”

This discovery means star formation began about 200 million years before the galaxy’s current state, and so studying the leftover dust brings astronomers closer to the origins of the Universe.

Carousel image: artist's impression of galaxy A2744_YD4
Credit: ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO and D. Coe (STScI)/J. Merten (Heidelberg/Bologna)
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