The Young Astronomers
Currently viewing the tag: "Galaxies"
NASA’s Chandra X-ray observatory has produced a spectacular image of the spiral galaxy M83:
Chandra’s view of M87 and SN 1957D Credit: NASA/CXC/STScI/K.Long et al.
The primary target of the image wasn’t the galaxy itself but a supernova remnant within – the remains of SN 1957D
This supernova remnant had previously been detected in both visible and the infra-red though had previously eluded detection in x-rays (Chandra’s first attempt to capture the object in 2000-2001 met with disappointment). This image is the end result of nearly eight and a half days of data collection using Chandra, a truly marathon effort (the observation was completed in stages during 2010 and 2011 rather than in one massive event).
The image show a wide range of X-rays, with low energy rays displayed in red, medium energy in green and those with the highest energies displayed here in blues.
The Chandra team has also produced an annotated version of the image showing the location of the remnant and you can see this below:
Credit: X-ray: NASA/CXC/STScI/K.Long et al., Optical: NASA/STScI
The type of X-ray emission detected from the remnant strongly suggests that it contains a rapidly spinning neutron star – a pulsar. This potentially makes it the youngest pulsar ever observed, positively confirmed as one just 55 years after it was formed (discounting the time it has taken the light to reach us here on Earth). It is potentially the youngest ever observed as there is another contender – SN 1979C – though as of yet astronomers aren’t quite sure if it is indeed a pulsar or a black hole.
M83 itself sits about 15 million light years from us in the direction of the constellation Hydra. It is one of the brightest galaxies visible from Earth and can be observed through binoculars.
M83 Credit: ESO/IDA/Danish 1.5 m/R. Gendler, S. Guisard and C. Thöne
You can read more here
NGC 2366 is a small, irregular dwarf galaxy 10 million light years away in the direction of the constellation Camelopardalis - the giraffe.
NGC 2366 Credit: NASAESA
[important]You can click on the image to view a larger version[/important]
The clearly visible blue region in the upper-right corner of the image is the star-forming nebula NGC 2363.
Broadly similar to the Milky Way’s satellite galaxies the Large and Small Magellanic cloud NGC 2366 may be small in comparison to many of the galaxies we are more accustomed to viewing in Hubble image though this doesn’t stop it from being a very active star factory indeed.
The smattering of active regions indicates that the galaxy is producing a great deal of the high mass blue stars (the blue smudges – and of course within NGC 2363).
The image was produced using Hubble’s infrared and green filters and so even though these regions appear blue they are actually a shade of red.
The image spans a distance of roughly 1/5 the diameter of the full moon though the galaxy itself is much too faint to be seen with the naked eye.
The view also captures a much more distant spiral galaxy which can be seen as the orange-brown structure in the upper middle portion of the image.
You can read more about the image here
3.8 billion light years away in the constellation Draco deep inside the centre of an inconspicuous galaxy, something happened at 12:57:45 on the 28th of March 2011 that flooded the SWIFT satellite’s sensors with x-rays, and in the process sent astronomers scrambling to get a glimpse with their ground and space-based observatories.
If you look at the light curve provided by SWIFT, the x-ray brightness fluctuates considerably over a period of days. You get the first massive burst, then it calms, and then you get some more bursts days after the original event. This is very different from GRBs, such events usually consist of a huge burst of x-rays and then a dimmer afterglow of a whole variety of radiation before fading from view over a period of hours at the most. So if it isn’t a GRB, then what is it?
The massive bursts happen to be coming from the centre of the galaxy, lighting up the heart of the galaxy with the power of 1 trillion suns; outshining the galaxy itself 100 times over. Like most of the galaxy population, a super massive black hole (SMBH) happens to lurk here. Could it be that the black hole has woken up? Active galaxies emit a huge amount of radiation, including X-rays, right across the electromagnetic spectrum after all.
With data from various surveys – including FERMI and ROSAT – astronomers have concluded that before this event there has been no sign of activity from the SMBH for the past 20 years at least, so for it to flare up without warning is very unusual!
So far the most popular theory with the most evidence suggests a main sequence star with a mass equivalent to our sun’s wandered too close to the gravitational grip of the SMBH; a monster weighing in at 107 solar masses. During a single pass it would have had to put up with one side of it being stretched and tugged at more than the other, until the gravitational pull was so powerful that the star started to get torn apart.
The matter from the disintegrated star has now settled to form a temporary accretion disk that provides fodder for the black hole. The material in the disk started to interact, and a mixture of friction and magnetic fields collimated the radiation into jets which we view as head-on, drowning out the host galaxy with its luminosity.
If this is indeed the case, the bursts of radiation seen with SWIFT and other observatories should cease after a period of months to just over a year. This would show that the star is slowly getting devoured or spat out from the accretion disk, until one day there will be no fodder for the black hole at all, and it will settle back down into its dormant state and probably won’t wake up again until the galaxy merges, or another star falls prey to its gravity well.
There is another theory I’ve picked up from Arxiv by Dokuchaev et al. which is rather more exotic:
Instead of a star being destroyed via accretion, something massively destructive happened to a star cluster near the centre of the galaxy… But first, let me focus on GRBs.
There are two types of Gamma Ray Bursts; short GRBS and long GRBs. So, what’s the difference?
Long GRBs are the most common. They’re likely to come from Type 2 supernovae, the type of supernova you get when a high mass star implodes, leaving only a core or a black hole behind. The insanely bright jets of gamma rays are thought to come from the poles of stars that are collapsing into black holes and last up to a few minutes.
Short GRBs are less common, and are likely to come from the merger of two neutron stars or a neutron star colliding with a stellar mass black hole. They last less than two seconds, but are still as destructive to anything that lies in their path as the Long GRBS.
The star cluster mentioned earlier would have a whole variety of stars to choose from, including stellar remnants such as the ones mentioned above. The stars with the most mass will migrate to the centre of the cluster, until eventually the gravitational pull of each star in the vicinity causes them to interact with each other rather destructively…
Neutron stars start to collide with each other and stellar mass black holes, creating plenty of Short GRBs as they go along. The many GRBs account for the repeating flares recorded by SWIFT and other observatories. In the period of two days 7% of the stars that make up the cluster collapsed into an accreting super massive black hole!
If this theory is correct the black hole won’t shut down any time soon like in the most popular theory, but will carry on for many years as it gains in mass over time from devouring the remainder of the star cluster and perhaps beyond.
However, I’m standing by the first theory 
Either way there’s some very interesting speculation surrounding this amazing object!
You can read more on this event here and here (both in PDF format) and on NASA.
The latest release from NASA’s WISE mission has shown that just over 200 previously unidentified high energy objects are likely to be blazars.
Artist's Impression of an active Blazar Credit:NASA/JPL-Caltech
A blazar is a form of active galactic nucleus (AGN) – a galaxy where the central black hole is ‘feeding’ on large amounts of material resulting in the release of huge amounts of radiation including two tight very bright jets.
The angle at which the AGN is situated relative to the Earth determines which form of AGN we observe even though all are tied to the same processes.
In the case of a blazar we are looking directly down the AGN’s jets you could even say right down the barrel of the gun!
AGN at various angles; Credit: Aurore Simonnet, SSU NASA E/PO.
As the AGN must be lined up almost exactly with Earth for a blazar to be observed they are understandably rare compared to the other forms of AGN which have a much larger range of possible viewing angles. That being said the WISE data has the potential to reveal several thousand more.
A team using the WISE data looked at 300 objects that had previously been detected as high energy gamma-ray sources by the Fermi Space Telescope, though up to now had remained unidentified.
Using WISE the team was able to observe these gamma ray hotspots in infra-red wavelengths and showed that just over half are most likely to be blazars. WISE had also observed 50 new blazars outside those Fermi oddities along with taking observations of more than 1000 previously identified blazar candidates.
One of the project leads, Francesco Massaro has explained that there may be several thousand more as of yet unknown blazars hidden within the WISE data that could be revealed using the techniques developed for this first sample.
An image of one of the new WISE identified blazars Credit:NASA/JPL-Caltech/Kavli
You can read more here
The ESA’s Planck Space Telescope completed its mission on Saturday.
The mission was designed to peer into the detail of the cosmic microwave background radiation (CMB) – the residual energy left after the Big Bang.
An artist's impression of the Planck spacecraft with a microwave background Credit: ESA
Planck also used its microwave detectors to gaze at the cold dust within our galaxy and beyond, detecting many new galaxy clusters in the distant universe. Some of these even appear to be interacting and merging to form even larger superclusters.
The first data from Planck was released last year and included the improved catalogue of galaxy clusters, though the first data set on its study of the CMB is yet to be released, though this will be made available to scientists outside the project in the early stages of 2013.
The mission was originally planned to make two surveys of the entirety of the sky over the space of 15 months. Planck performed better than expected and completed five surveys over 30 months, double the original mission expectancy.
The data released so far also reveals that stars in the universe were being formed at one thousand times the current rate, a fairly phenomenal statistic!
The telescope is equipped with two instruments:
- The High Frequency Instrument or HFI
- ow Frequency Instrument or LFI
These two instruments work in tandem to build up a highly accurate map of the CMB. Unfortunately the HFI is now offline as the spacecraft depleted the last of its coolant supply and has now warmed above the critical temperature required for the useful opperation of the detector. The LFI however is still in working order and will continue to provide additional data over the rest of the year.
No doubt the data from Planck will reveal many new interesting features of the universe over the next few years, I for one am very excited!
You can read more here.
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