for astronomers Omega Centauri has been an outcast amongst globular clusters for
a long time a new result obtained by the nasa/esa Hubble Space Telescope and the
Gemini Observatory provides a surprising explanation for Omega Centauri
specularity z--
this is the hubblecast news and images from the nasa/esa Hubble Space Telescope
travelling through time and space with our host dr. J aka dr. Joe Liske welcome
to the hubblecast today's cosmic guest star is a very
special object Omega Centauri has long been known to be the largest and
brightest globular cluster visible in the night sky now the globular cluster
is a nearly spherical group of tens to hundreds of thousands of old stars
tightly bound together by gravity and found in the outskirts of many galaxies
including our own Milky Way beautiful but enigmatic Omega Centauri has always
been a bit of a puzzle to astronomers
Omega Centauri lies in the constellation of Centaurus and is visible from Earth
with the naked eye it's one of the favourite celestial objects for southern
hemisphere stargazers appearing almost as large as the full moon when seen from
a dark sight exactly what type of object Omega Centauri is has long been a
contentious topic it was first listed in Ptolemies catalogue as a single star
nearly two thousand years ago in 1677 Edmund Halley reported it as a nebula in
the 1830s the English astronomer John Herschel was the first to recognize it
as a globular cluster a classification that it is kept ever since
Omega Centauri has several characteristics that separate it from
other globular clusters compared to a run-of-the-mill globular Omega Centauri
has a highly flattened shape it rotates faster and it includes several
generations of stars which is an unusual feature for globulars which normally
contain only a single generation of old stars
moreover Omega Centauri is almost 10 times more massive than other globular
clusters almost as massive as a small galaxy now new images obtained with the
advanced camera for surveys onboard the nasa/esa Hubble Space Telescope and data
obtained with the GMO spectrograph at the Gemini Observatory show that Omega
Centauri appears to be harboring an elusive intermediate-mass black hole at
its centre the black hole was discovered after astronomers measured the motions
and brightnesses of stars at the center of Omega Centauri they found that these
stars were moving much faster than expected given their total number and
brightness such behavior clearly indicates the existence of something
extraordinarily massive at the center of the cluster the intense gravitational
field of a black hole with a mass of 40,000 solar masses provides just the
kick necessary to explain the measurements
this is dr. Yvonne Ooyala of the Max Planck Institute for extraterrestrial
physics in Germany so ever you were the lead author on the
study how did you find this black hole what we found these black hole was by
looking at the Hubble image and measuring how many stars are there at
the very center of this cluster and then we take the Jimo spectrograph and
measure velocities the velocities of these stars what we find is that the
velocities are much higher than what we would expect just from the stars and
that implies that there's an extra man of matter which is it means that we
found a black hole and what's so special about this black hole the very special
thing about this black hole is that it has 40,000 solar masses in size so that
means it's a lot bigger than the stellar-mass black holes are we find in
our galaxy but it's much smaller than the supermassive black holes are we
found at the center of galaxies so it means that nature makes black holes in a
continuous mass range not just in small and big sizes so what's the big deal why
is it so important well first of all this is only the second black hole that
we find in a globular cluster so that is a very nice reassuring thing but also we
know that there are seeds required to grow the supermassive black holes from
scratch and if we find many of these then that would be a very nice source
for these seeds to grow to grow the supermassive black holes
one implication of this discovery is that it is very likely that Omega
Centauri is not a globular cluster at all but rather some kind of dwarf galaxy
that has been stripped of its outer stars and dark matter as some scientists
have suspected for a few years more than two thousand years after Omega Centauri
was wrongly classified as a star it's true nature is finally coming to light
but I wonder does Omega Centauri have more surprises in store for us this is
dr j signing off for the hubblecast once again nature has surprised us beyond our
wildest imagination
at one time