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Milky Way’s 'missing satellites'

Two researchers have explained why galaxies like our Milky Way have so few satellites around them – the ‘missing satellites’ problem. They have revealed for the first time the existence of a new signature of the birth of the first stars in the Milky Way.

india Updated: Oct 20, 2011 13:58 IST

Two researchers from Observatoire Astronomique de Strasbourg have explained why galaxies like our Milky Way have so few satellites around them – the ‘missing satellites’ problem.

They have revealed for the first time the existence of a new signature of the birth of the first stars in the Milky Way.

Milky WayMore than 12 billion years ago, the intense ultraviolet light from these stars dispersed the gas of our galaxy’s nearest companions, virtually putting a halt to their ability to form stars and consigning them to a dim future.

Now Pierre Ocvirk and Dominique Aubert, members of the Light in the Dark Ages of the Universe (LIDAU) collaboration, have explained why some galaxies were killed off, while stars continued to form in more distant objects.

The first stars of the Universe appeared about 150 million years after the Big Bang. Back then, the hydrogen and helium gas filling the universe was cold enough for its atoms to be electrically neutral.

As the ultraviolet (UV) light of the first stars propagated through this gas, it broke apart the proton-electron pairs that make up hydrogen atoms, returning them to the so-called plasma state they experienced in the first moments of the Universe.

This process, known as reionization, also resulted in significant heating, which had dramatic consequences: the gas became so hot that it escaped the weak gravity of the lowest mass galaxies, thereby depriving them of the material needed to form stars.

It is now widely accepted that this process can explain the small number and large ages of the stars seen in the faintest dwarf galaxy satellites of the Milky Way.

The new model appears to be a close match to observations of our galaxy and its neighbourhood and suggests that the first stars of our galaxy played a major role in the photo-evaporation of the satellite galaxies’ gas, added Dr. Ocvirk.

The study was published in the journal Monthly Notices of the Royal Astronomical Society.