A major revision is required in our
understanding of our Milky Way Galaxy according to an international team led by
Prof Noriyuki Matsunaga of the University of Tokyo. The Japanese, South African
and Italian astronomers find that there is a huge region around the centre of
our own Galaxy, which is devoid of young stars. The team publish their work in
a paper in Monthly Notices of the Royal Astronomical Society.
The Milky Way is a spiral
galaxy containing many billions of stars with our Sun about 26,000 light years
from its centre. Measuring the distribution of these stars is crucial to our
understanding of how our Galaxy formed and evolved. Pulsating stars called
Cepheids are ideal for this. They are much younger (between 10 and 300 million
years old) than our Sun (4.6 billion years old) and they pulsate in brightness
in a regular cycle. The length of this cycle is related to the luminosity of
the Cepheid, so if astronomers monitor them they can establish how bright the
star really is, compare it with what we see from Earth, and work out its
distance.
Despite this, finding Cepheids in the
inner Milky Way is difficult, as the Galaxy is full of interstellar dust which
blocks out light and hides many stars from view. Matsunaga's team compensated
for this, with an analysis of near-infrared observations made with a
Japanese-South African telescope located at Sutherland, South Africa. To their
surprise they found hardly any Cepheids in a huge region stretching for
thousands of light years from the core of the Galaxy.
Noriyuki Matsunaga explains: "We
already found some while ago that there are Cepheids in the central heart of
our Milky Way (in a region about 150 light years in radius). Now we find that
outside this there is a huge Cepheid desert extending out to 8000 light years
from the centre."
This suggests that a large part of our
Galaxy, called the Extreme Inner Disk, has no young stars.
Co-author Michael Feast notes: "Our conclusions are contrary to other
recent work, but in line with the work of radio astronomers who see no new stars
being born in this desert."
Another author, Giuseppe Bono, points
out: "The current results indicate that there has been no significant star
formation in this large region over hundreds of millions years. The movement
and the chemical composition of the new Cepheids are helping us to better
understand the formation and evolution of the Milky Way."
Cepheids have more typically been used
to measure the distances of objects in the distant Universe, and the new work
is an example instead of the same technique revealing the structure of our own
Milky Way.
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