The Lonely Blackhole

Unique mid-sized black hole is the lonely survivor of a shredded galaxy.

This is the Hubble Telescope's latest and clearest yet image of the galaxy ESO 243-49. Astronomers have been watching this galaxy for a while now, because it's likely the only known medium-sized black hole in the sky right now.

The black hole at the center of this galaxy is known as HLX-1. Located 290 million light-years away, this black hole appears to fit somewhere right between the small black stars that form when a giant star collapses and the supermassive black holes that are found at the centers of galaxies. No one have an idea on how these supermassive black holes come to exist. The best explanation is that they are formed by the repeated collisions of galaxies, which smashes black holes together to form larger and larger mergers. For that to work, we should be seeing black holes that are still in the middle of the transition from small to supermassive.

Astronomers are eager to learn more about its particular origins. Now, thanks to Hubble, it is known that it is surrounded by a bunch of young massive blue stars that form a cluster some 250 light-years across. Hubble scientist Sean Farrell explains:

"Before this latest discovery, we suspected that intermediate-mass black holes could exist, but now we understand where they may have come from. The fact that there seems to be a very young cluster of stars indicates that the intermediate-mass black hole may have originated as the central black hole in a very-low-mass dwarf galaxy. The dwarf galaxy might then have been swallowed by the more massive galaxy, just as happens in our Milky Way."

The cluster is a crucial clue because there's no way it could have formed under normal circumstances so far from the center of the galaxy. This suggests that they were likely formed when HLX-1 was captured by its current galaxy in a collision with its original home, most likely a dwarf galaxy. The black hole was the central black hole in this tiny galaxy, but its stars were ripped away in the collision, which also would have compressed the surround gas and kicked off the star formation that created these blue giants.

This particular collision was fairly recent, the stars are only about 200 million years old and HLX-1 is still just beginning the process of feeding and growing.

Hidden Pluto

Pluto is about forty times the distance from the Sun as Earth. But our Solar System is over 50000 times across that which means it could be hiding some huge blackbody.

In recent years, astronomers have discovered a bunch of planets located at least 100 astronomical units away from their host stars. These planets are gas giants. The problem is that they dont emit light well unless they are close to something bright like the sun. This is something very different the dwarf planets like Pluto and Eris discovered in our solar system's Kuiper Belt and beyond.

There's almost no chance that these giant planets could have formed as part of their host star's planetary disc, considering their immense distance away. That strongly suggests that these are former rogue planets captured by the star's gravity. Scientists at Harvard-Smithsonian Center and Peking University's Kavli Institute tries to figure out just how often we can expect stars; potentially including those like our own Sun; to capture these giant wandering planets.

Quoted by ScienceNOW report:

"Because most stars are born with others, Perets and Kouwenhoven ran computer simulations to see what happens when a star cluster contains free-floating planets. If the number of free-floating planets equals the number of stars, then 3% to 6% of the stars succeed in capturing a planet, and some stars capture two or three. Most of the captured planets end up hundreds or thousands of times farther from their stars than Earth is from the sun. Furthermore, most captured planets have orbits tilted to those of native-born planets, and half the captured planets revolve around their stars backward."

Their work depends on having a good grasp of how many rogue planets there really are, and we can't be sure our current estimates, which suggest there area as many wandering planets as there are stars, is accurate. But if these results are accurate, then our Sun, whose mass is slightly above average, had a real chance of capturing one or more planets eons ago.

The chances aren't huge but probably only a few percent higher. If their numbers are accurate, then the possibility of such a planet definitely exists.

What do you see in this picture?

This is not a rorschach test for psychology but an image of NGC 3324 or whatever you are imagining of this silhollet .

The fierce ultraviolet radiation given off by the young stars, NGC 3324, has carved this giant cavity in space. Because of the boundary between different gases it looks an awful lot like a person's profile.

The astronomers at the La Silla Observatory in Chile's Coquimbo Region have dubbed this the Gabriela Mistral Nebula. So how was this boundary created between the different parts of the nebula?

A deposit of gas and dust in the NGC 3324 region fueled a burst several millions of years ago and led to the creation of several hot stars that are apparent in the picture. Stellar winds and intense radiation from these stars have blown open a hollow in the surrounding gas and dust. The ultraviolet radiation from the hot stars knocks electrons out of hydrogen atoms thus ionizing it, which are then recaptured, leading to a crimson colored glow as the electrons jumps through the energy levels, showing the extent of the local diffuse gas. Other colors come from other elements, with the characteristic glow from ionized oxygen making the central parts appear greenish-yellow.

Shrinking of the North Star

The North Star, or Polaris as astronomers calls it, has been guiding sailors and many others at night for centuries. Now astronomers found out that all is not well with its light cycles, it turns out that Polaris is losing mass equivalent to the earth each year. The idea was proposed by Hilding Neilson and his team at the University of Bonn. The researchers weighed Polaris which is a supergiant main star in the Polaris multiple star system by monitoring how its light cycles dims and brightens.

By detecting a star's light cycle one can know the mass of the star. How this works is like most supergiant stars like our sun is made up of gases in the layers around the core where fusion occurs. The gravitational force of the star pulls the outermost gas inward creating an opaque layer just below the surface. This surface acts like a pressure tank which hold light in. Once it reaches its limit it releases the light build up at once like a shaken bottle of coke. The light buildup will heat up the opaque layer expanding it and becomes transparent. After energy is disperse from the heated opaque layer it will be pulled down again the cycle continues.

The thing is that Polaris's light cycle hasn't remained constant. Observations made in 1844 reveal Polaris's pulse used to be 12 minutes slower than it is now, and 168 years of data suggest that Polaris's pulse regularly decreases by about 4.5 seconds each year. The best explanation from Neilson, is that Polaris is dispersing an earth's worth of mass into space every year, which would throw off the inner workings of the light cycle just enough to account for this big drop.

The good news is that Neilson says this mass loss is likely to be temporary in the star's life. The star isn't going to disappear anytime soon with this method of dispersing mass. Still this wont matter because Polaris isnt going to be our north star anymore. In another 1000 years Gamma Cephei will replace the alignment where Polaris is. So in the future we can still be certain that we can still navigate the sea by stars.


http://m.iopscience.iop.org/2041-8205/745/2/L32