The NASA/ESA Hubble Space Telescope has captured
a spectacular image of NGC 3603, a giant nebula hosting one of the most prominent
massive young clusters in the Milky Way. This is a splendid location for continuing
our detailed studies of stellar birth in star forming regions. Welcome to the Hubblecast! Today we are going to travel to the heart
of a massive cluster of young stars that lies deep inside a vast nebula of gas and dust. The nebula is called NGC 3603 is located about
20,000 light-years from Earth in the Carina spiral arm of our own Milky Way galaxy. Now it turns out that the nebula is actually
the nursery of the star cluster. It is thought that the nebula contains hundreds
of thousands of solar masses worth of gas, and only about one million years ago, some
of that gas collapsed in on itself and formed probably all of the stars in the
cluster at more or less the same time in a massive burst of star formation. Today we see the result as a glittering collection
of stars surrounded by a dense cloud of hydrogen gas. In this new detailed image from Hubble we
can see thousands of young blue stars sparkling against their maternal nebula. But this is not as tranquil a place as you
might think. Some of the action is still going on. The strong ultraviolet radiation and the winds
from these newborn stars are shaping and sculpting the surrounding gas, carving out a huge cavity
into the nebula. A team of astronomers was able to use the
Hubble Space Telescope to peer into the heart of a star forming region which was first observed
in 1834 by Sir John Herschel, the son of world-renowned astronomer Sir William
Herschel. They were able to make detailed observations
of stars whose masses differ but whose ages are similar. Because of this fact astronomers were able
to study a wide range of stars at different points
in their respective life cycles and make comparisons with other similar star clusters. [Music]
The new Hubble image is full of interesting objects for astronomers to study. Here at the top right of the image we see
a handful of Bok Globules. These objects were first observed in the 1940s
by astronomer Bart Bok. They are some of the coldest objects in the
Universe and they are dense clouds of gas and dust
(of around ten to fifty solar masses) and they are collapsing to form new stars. Around the cluster near the densest part of
the nebula we see these huge pillars of gas pointing away from cluster’s core. These were shaped by the massive young cluster’s
stars and eventually they will be dispersed into interstellar space. One of the most interesting objects in the
image is this seemingly innocuous bright star. The star, designated Sher 25, and it is actually
a blue supergiant nearing the very end of its life. Astronomers think that in the not too distant
future Sher 25 will explode as a tremendous event
like supernova 1987A which has been observed by Hubble on many occasions. In doing so it will seed space with the heavy
elements necessary for planet formation. Perhaps it will even trigger a new wave of
star formation in a nearby nebula. For now though astronomers using the Hubble
are interested in the stars within the massive young cluster at the heart
of NGC 3603. Several stars at the cluster’s core have
caused astronomers to be deceived. The huge stars in the innermost regions of
the cluster appeared to be far more massive than our current theoretical limits dictate. Nothing escapes the sharp eye of Hubble though
as it was able to show that these stars are in fact the light from several stars blended
together. They appear as one star but are actually composed
of two or even three components. This agrees well with previous observations
of these apparently ‘heavyweight’ objects as composed of several stars of around 80
to 120 solar masses each. The new Hubble image is full of amazing detail. Not only are we seeing a whole cluster of
stars just one million years after its birth. But there is also one star that is about to
go supernova in a gigantic explosion that will be seen across large parts of the Galaxy. In NGC 3603 we are literally seeing the birth
and death of stars right before our very own eyes. So, this apparently picturesque stellar nursery
is in fact the site of some pretty extreme astronomy! New Hubble observations of the massive globular
cluster NGC 2808 provide evidence that it has three generations of stars instead
of one as current theories predict. Globular clusters are the homesteaders of
our Milky Way Galaxy, because they were born during our Galaxy’s formation. They are compact swarms of typically hundreds
of thousands of stars that have been held together by gravity. Astronomers have long thought that globular
clusters experienced a single “baby boom” of star formation at the beginning of their
lives and then settled into a rather quiet existence. New observations by the NASA/ESA Hubble Space
Telescope is showing that this idea may be too simple. The Hubble analysis of the massive globular
cluster NGC 2808 is providing evidence that instead of having one baby boom of star formation,
star birth went “boom, boom, boom”, creating three generations of stars early on in the
cluster’s life. The astronomers used Hubble’s Advanced Camera
for Surveys to measure the brightness – seen along this axis - and the colour of the
cluster stars – seen here, with blue to the left and red to the right. The measurements showed three distinct populations,
with each successive generation appearing slightly bluer. This colour difference suggests that successive
generations contain a slightly different mix of some chemical elements. Astronomers commonly believed that globular
clusters produced only a single stellar generation, because the energy from that first batch of
stars cleared out the remaining gas needed for more stars. But a hefty cluster like NGC 2808, which is
two to three times more massive than a typical globular cluster, may have
enough gravity to hold on to that gas. Although the astronomers have searched only
two globular clusters for multiple stellar generations,
they say this may be a typical occurrence in other massive clusters as well. Now, no one is going to take the radical step
of suggesting that previous work on other clusters is no longer valid. But this discovery does show that the study
of stellar populations in globular clusters may be heading in a new direction. The team plans to use ESO’s Very Large Telescope
in Chile to study the chemical composition of NGC 2808. This may offer further evidence that the stars
were formed at different times and may yield clues to how they formed. The team will also use Hubble to hunt for
multiple generations in about 10 more hefty globular clusters. 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’s peculiarities. 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, A globular cluster is a nearly spherical
group of typically tens or hundreds of thousands of stars tightly bound together by gravity,
found on 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 is one of the favourite celestial objects
for southern hemisphere stargazers, appearing almost as large as the full Moon
when seen from a dark site. Exactly what type of object Omega Centauri
is, has long been a contentious topic. It was first listed in Ptolemy’s catalogue
as a single star nearly two thousand years ago. In 1677, Edmond 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 has 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 by the GMOS spectrograph at Gemini Observatory
show that Omega Centauri appears to harbour 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 centre of Omega Centauri. They found that these stars were moving much
faster than expected given their total number and brightness. Such behaviour clearly indicates the existence
of something extraordinarily massive at the centre 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. One implication of this discovery is that
it is very likely that Omega Centauri is not a globular cluster at all,
but some sort 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?
