NASA!
And now
back
to business.
This week, astronomers using the VLT Survey Telescope at ESO's Paranal Observatory have
observed one of the largest stars in the known universe as it is about to die.
Astronomers using this telescope have been surveying our galaxy using a special filter
to detect nebulae of ionized hydrogen in search of ejected material from evolved stars.
Looking at the most massive cluster of stars in our galaxy, known as Westerland 1, which
is home to a large number of rare, evolved high mass stars they made a remarkable discovery.
Westerland 1 is about 16,000 light years from Earth in the southern constellation of Ara
(The Altar), and has remained largely unstudied for many years due to high interstellar extinction
(absorption) in its direction.
Basically, the gas of the galaxy between us and this cluster is in the way.
Westerlund 1 is believed to have formed in a single burst of star formation, which implies
the stars that make it up have similar ages and compositions.
When the astronomers studied the images of Westerlund 1 from VLT, they spotted something
truly unique.
Around one of the stars, known as W26, they saw a huge cloud of glowing hydrogen gas,
shown as green in this new image.
Such glowing clouds are ionised, meaning that the electrons have been stripped away from
the atoms of hydrogen gas.
Clouds of this type are rarely found around massive stars and are even rarer around red
supergiant stars such as W26 — this is the first ionised nebula ever discovered around
such a star.
W26 itself would be too cool to make the gas glow so the astronomers speculate that the
source of the ionising radiation may be either hot blue stars elsewhere in the cluster, or
possibly a fainter, but much hotter, companion star to W26.
On investigating this star in more detail the researchers realised that this star is
probably the largest star ever discovered, with a radius 1500 times larger than the Sun
and is also one of the most luminous red supergiants known.
Such large and luminous massive stars are believed to be highly evolved, all of which
suggests that W26 is coming towards the end of its life and will eventually explode as
a supernova.
Next, two international teams of astronomers interested in studying the jets from supermassive
black holes at the centers of galaxies have used the Atacama Large Millimeter/submillimeter
array or ALMA, to take a closer look.
These two teams used ALMA to probe black hole jets at different scales: a nearby and relatively
quiet black hole in the galaxy NGC 1433 and a very distant and active object called PKS
1830-211.
Now remember supermassive black holes have masses up to several billion times that of
our sun and lie at the hearts of most galaxies.
These black holes got so big by swallowing enormous amounts of matter from their surroundings
and shooting tiny fractions of that matter back out through extremely powerful jets.
In one of the black holes, the one in NGC 1433, ALMA found a surprising spiral structure
in the molecular gas close to the center of the galaxy.
And according to the astronomers, "This explains how the material is flowing in to fuel the
black hole.
With the sharp new observations from ALMA, we have discovered a jet of material flowing
away from the black hole, extending for only 150 light-years.
This is the smallest such molecular outflow ever observed in an external galaxy."
The discovery of this outflow, which is being dragged along by the jet from the central
black hole, shows how such jets can stop star formation and regulate the growth of the central
bulges of galaxies
In the other black hole, the one in PKS 1830-211, that team also looked at a SMBH with a jet,
but this was a much brighter and more active one in the early Universe.
It is unusual because its light was gravitationally lensed as it passed a massive intervening
galaxy on its way to Earth, and was split into two images.
Every once in a while, a supermassive black hole suddenly swallows a huge amount of matter,
and that increases the power of the jet and boosts the radiation up to the highest energies.
This team has caught by chance, one of those events as it happens.
Here is what they say:
"The ALMA observation of this case of black hole indigestion has been completely serendipitous.
We were observing PKS 1830-211 for another purpose, and then we spotted subtle changes
of colour and intensity among the images of the gravitational lens.
A very careful look at this unexpected behaviour led us to the conclusion that we were observing,
just by a very lucky chance, right at the time when fresh new matter entered into the
jet base of the black hole,"
These observations are just the start of ALMA's investigations into the workings of jets from
supermassive black holes and this instrument promises to provide us with some very valuable
contributions into this in the near future.
Well, that's it for this week Space Fans.
Thank you for watching and as always, Keep Looking Up!