Friday, 17 November, 2017

Ancient stardust sheds light on the first stars

This artist’s impression shows what the very distant young galaxy A2744_YD4 seen when the Universe was just 4% of its current age might look like. Image ESO  M. Kornmesser Cosmic stardust from the dawn of the universe detected by Alma telescope
Garry Little | 12 March, 2017, 00:26

When stars die in supernova explosions, they leave behind clouds of dust and gas that can later form new stars, planets and other celestial bodies.

Astronomers used the ALMA telescope in Chile to observe the galaxy A2744_YD4. This galaxy was observed shortly after its formation and is the most distant galaxy in which dust has been detected. The ALMA observations are also the most distant detection of oxygen in the Universe.

The cycle of stellar birth and recycling continued, until about 10 billion years ago, Pop I stars began to form.

The galaxy A2744_YD4 was discovered by the Atacama Large Millimeter Array (ALMA), a radio telescope located in Chile. An global team led by Nicolas Laporte of the University College of London spearheaded the search, then used ESO's Very Large Telescope to follow up and confirm the distance of A2744_YD4.

The scientists revealed that this galaxy looks to us as it was during the period when the first stars and galaxies were formed, when the universe was only 600 million years old.

A2744_YD4's cosmological "timestamp", as given by its redshift, falls within the estimated age range for the Epoch of Reionization, which occurred somewhere around a redshift of 10, when the universe was about 400 million years old.

ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO and D. Coe (STScI)/J.

Cosmic dust is mainly composed of silicon, carbon and aluminum, in grains as small as a millionth of a centimeter across. This is due in part to a gravitational effect from a large cluster of galaxies between us and A2744_YD4 that bends the light from the distant galaxy and acts as a giant magnifying lens.

The ALMA observations also detected the glowing emission of ionized oxygen from A2744_YD4. The abundance of dust in A2744_YD4 means the first massive stars formed very early in the galaxy's history, about 200 million years before the light ALMA is observing now. Determining the timing could be the key to "one of the holy grails of modern astronomy".

Galaxy A2744_YD4 appears to hold enough of this stardust to make 6 million suns, while the mass of the galaxy's stars add up to 2 billion times the mass of the sun. Stars were forming there at a rate of 20 solar masses per year - compared with one star a year in the current Milky Way. The galaxy has been named as A2744_YD4 is still surrounded by a lot of stardust left behind in the wake of the death of earlier stars in its place.

This provides a great opportunity for ALMA to help study the era when the first stars and galaxies "switched on" - the earliest epoch yet probed. You, the screen you are now reading these words on, the chair you are sitting on and the planet you live on are all the end result of 13.8 billion years of cosmic evolution - a process that began with the birth and death of the first stars.

"With ALMA, the prospects for performing deeper and more extensive observations of similar galaxies at these early times are very promising", says Ellis.

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