Tantrums in Cosmic nurseries

Three space telescopes have been working hard to produce results, and today those results all seemed to be concerned with the building blocks of the largest objects in our local region.

Firstly to the Herschel Infrared Space Telescope. Followers of this new eye on the sky will know that one of the most interesting uses is the ability to penetrate dust that scatters visible light, but merely dims infrared radiation a little. This enables us to x-ray regions that appear dark in visible light and see what hides within and behind them. In a recent result, Herschel turned to the reflection nebula NGC 1999. Located 1,500 light years from Earth in the constellation of Orion, it shines by reflecting light from the variable star V380 Orionis. But in common with other nebula in the area, it has black patches, which have in the past turned out to be dust. This time, Herschel had a peek and… nothing. Still black. Astronomers followed up with observations in all kinds of wavelengths, still nothing. In fact it looks like the black patch is actually due to an absence of stuff rather than a lot of light blocking stuff. Scientists believe the area might be a place where new born stars are pushing away the surrounding gas and dust with their new stellar winds and radiation.

In another nebula, more interesting things have been brewing. In 2006, a team led by Ian Howarth of my own university (I worked as his marker for a short while, that’s the extent of my involvement…) discovered an unusual bright blue star in a field of not very bright or blue stars on the edge of the Tarantula Nebula also known as 30 Doradus. The Hubble Space Telescope has since turned the new Cosmic Origins Spectrograph to the loner and measured its proper motion as well as other properties. Proper motion is the motion the star apparently makes through the night sky due only to its real motion in space. That two-dimensional velocity can then get used with the Doppler shift to find the three dimensional motion of the star through space. 30 Doradus is 170,000 light years from the Earth, making observations pretty difficult, but this star is bright and it has been suspected that the star is bright because it is big and it is young.

The star was used by the COS team to help calibrate the spectrometer, but as they did so, they discovered the spectrum showed the stellar wind to be flowing from the surface fast and hard – providing some evidence that the star was in fact the big, young thing suspected. Archived optical images also showed the star to be at one end of an egg-shaped chamber of evacuated gas pointing toward the cluster R136. Astronomers turned to observations by the European Southern Observatory’s Very Large Telescope, which had been conducting a survey of the region. The VLT results showed that the motion of the star was constant, unlike the orbital motions of nearby stars and that the star shone as one bright object, not the combined light of two unresolved stars, again suggesting a large, bright thing.

Putting all the pieces together, astrophysicists determined that the star was around 90 solar masses and probably formed in the star cluster R136 before getting kicked out. Of the two mechanisms available for kicking a star this size out of a cluster; the supernova of something big and close by or something even bigger than 90 solar masses flinging it out due to gravitational interactions – the latter suggestion seems to hold sway, firstly because there’s no evidence of such a supernova and secondly, the cluster is believed to be too young for a supernova to have gone off even in the short lived very massive stars that are believed to be in there, and which must be in there for a 90 solar mass star to be thought tiny enough to be kicked out. Reports of this have been splashed across the web, this from ESA, this from Universe Today, this from Discovery (with diagram of star getting kicked out) and this from Hubble itself.

The story was also reported here in Astronomy Now, along with another similar story. This one concerns a student going through x-ray sources identified by the Chandra X-ray space telescope. The catalogue of sources they used should’ve picked up signals from the supermassive black holes at the centres of any galaxies in the field of the observations the catalogue was based on. These black holes shine in x-rays through material falling into them releasing energy as radiation, material in the accretion disc getting accelerated and material in any jets meeting magnetic fields. Undergraduate student Marianne Heida of the University of Utrecht decided to do her final year project on cross matching these sources to optical light images of galaxies – see which black hole slots into the middle of which galaxy. She studied hundreds of thousands of sources, but one stood out. A source that seemed to lie away from the centre of its host galaxy. Her supervisor believes the reason for this is the black hole is the result of a merger between two intermediate sized black holes and the gravitational recoil from the merger has flung it out from its home in the middle of the galaxy.

As an addendum, Chandra has also been working with the XMM-Newton X-ray Space Telescope to look for Missing Matter. Missing Matter isn’t the same as Dark Matter, it comes about from observations of distant galaxies, working out how much ordinary matter is in them and then looking at today’s galaxies and realising we’re missing about half of it. One idea is that the galaxies are leaking out matter from expanding supernova shells, stellar winds and the like, this is called the Warm-Hot Intergalactic Medium. This stuff should be pretty thin as far as gases go and pretty transparent, making it very hard to see. So working out how much should be present in a known big cluster of galaxies called the Sculptor Wall, located 400 million light years away between us and a known active galactic nucleus, itself located 2000, million light years from us, astronomers turned both the x-ray space telescopes on the AGN to see if emitted x-rays are being absorbed by oxygen atoms in the WHIM. The results suggest that they are by the amounts required for the WHIM to contain the missing matter. Although there have been some detections here and there of the bulk of the WHIM (and good detections of bits of it at energies where only a little of it is thought to be), this is the first observation that has been replicated by another telescope in the same temperature range.


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