For many years astronomers have debated and speculated about the existence of intermediate mass black holes. Well an answer to the question may now be available. It looks as though one of these mysterious types of black holes has been discovered in one of the Milky Way’s globular clusters. However, this discovery may not have all the answers to the mystery.

For many years the only kinds of black holes that have been found are stellar sized ones and super massive ones. Stellar sized black holes form as a result of the death of a massive star and can range up to maybe 50 solar masses. Super massive black holes reside at the center of almost all galaxies and weigh millions if not billions of solar masses. But observations were lacking for any black holes in between these sizes.

Globular Clusters are dense formulations of stars that orbit in the outskirts of a galaxy. They reside in what is known as the halo of the galaxy. They tend to be very old and are generally no longer creating new stars. They are fairly common, we know of about 200 hundred that belong to the Milky Way.

So it was in the globular cluster known as Omega Centauri that this intermediate black hole is thought to reside. Omega Centauri is one of the largest and most massive clusters belonging to the Milky Way, and is about 17,000 light years from earth. Using NASA’s Hubble space telescope and the Gemini observatory in Chile astronomers were able to note that the stars at the center of the cluster were orbiting something with very fast speeds. These fast speeds and the absence of anything we can see suggests it is a black hole that the stars are orbiting. The astronomers then used theoretical models combined with this data to calculate the mass of this black hole at about 40,000 solar masses.

This is actually the second discovery of a medium sized black hole suggesting the first was not just a fluke and that they may be common. However, no theory currently exists to explain why they exist, that is, to explain how they could have formed. However, there existence might be important for the theory of how super massive black holes form. One of the current theories states that in an early galaxy a “seed” black hole would be needed of about this size. The black hole would feed to grow to super massive size.

However, one issue might be that Omega Centauri is not a normal globular cluster, and many theorize that it is actually the remnant of a dwarf galaxy that was gobbled up by the Milky Way. Models that compare data of galaxy mass with super massive black hole mass show that a dwarf galaxy like the one predicted for Omega Centauri would have had a black hole of this size. So this would suggest not that these intermediate black holes are the seeds for super massive ones but actually play the same role as the super massive ones on a smaller scale.

More of these intermediate sized black holes will need to be discovered before any questions about formation or purpose can be answered.

There are many objects in the universe that have jets of material exploding from them. A few examples are neutron stars, black holes, quasars, and protostars. Well now we can add brown dwarfs to that list. One wonders what causes these jets and if brown dwarfs can have them what’s next?

A brown dwarf is like a failed star. It’s cool and small, with a mass range of between 10 to 90 Jupiter masses. These objects are not massive enough to start nuclear burning like normal stars. They can be hard to observe since they are so small and don’t give off nearly as much light as a normal star. There is some debate about how to distinguish a brown dwarf from a giant planet like Jupiter. There are some differences; they all have about the same radii so if the mass is higher than about 10 Jupiter masses, they have a higher density and are usually not considered a planet. Also with brown dwarfs water is always found in a gaseous state where in giant planets it condenses to ice; also planets usually have ammonia in their atmospheres while brown dwarfs do not.

Now the brown dwarf called 2MASS1207-3932 has a mass of about 24 Jupiter masses with a companion planet of about 5 Jupiter masses. This brown dwarf also has a disk around it like that seen in young stars. This is the smallest object ever observed to have a jet. The jet is moving at a speed of a few kilometers per second and stretches about 1 billion kilometers; it is also much smaller and less bright than jets seen in regular stars. Astronomers had observed jets from one other brown dwarf, so with this new discovery a pattern is emerging. Its discovery suggests that these brown dwarfs form in a similar manner to normal stars but also that outflows are driven out by objects as massive as hundreds of millions of solar masses down to Jupiter-sized objects.

Astronomers were not able to observe the jets directly. Astronomers had to use the powerful Very Large Telescope (VLT) , and only an instrument called UVES could provide the sensitivity and resolution required to “see” the jet. The results highlight the incredible level of quality of instruments available today. With ever more powerful and sensitive instruments we are observing more of these faint objects and are able to learn much more about brown dwarfs, their properties, and how they develop.

This discovery tells us more about the development of brown dwarfs, but also raises some new questions. Does this mean that giant planets also have jets that we haven’t detected yet? If not, why not? What is the cut off threshold between the two? Also, what role exactly do these jets play in the life of the brown dwarf? If not all brown dwarfs have jets, what are the resulting differences between ones that do and ones that don’t? Hopefully, as we are able to observe more of these objects with our better instruments we will learn the answers to these questions.

Two NASA scientists have found the smallest, or lightest weight, black hole ever yet discovered. The black hole is in the binary system, XTE J1650-500, which is in the constellation Ara in the southern hemisphere. The mass of the black hole is only 3.8 solar masses. This beats the previous record holder of 6.3 solar masses. The black hole was discovered earlier as part of the binary with a normal star and was known to be lightweight but its exact weight was not known until recently with the use of a new method.

This new method uses a relationship between the black hole and the inner part of the surrounding in falling gas and material. Hot gas piles up around the black hole as it falls in and heats up giving off x-rays. The x-ray’s intensity varies in a regular pattern, called the quasi-periodic oscillation, or QPC. Astronomers discovered the congestion zone is closer to smaller black holes and therefore makes the QPC change more quickly. To measure the black hole masses, astronomers used archival data from RXTE, which has made exquisitely precise measurements of QPO frequencies in at least 15 black holes. Using this method they measured the mass of XTE J1650-500 as 3.8 solar masses with a margin of error of only half a sun.

This value is well below those measured for other standard black holes. Now there is a threshold value below which a dying star will become a neutron star instead of a black hole. It is thought to be between 1.7 to 3 solar masses. However, with this new discovery and method of detection this boundary could be in question. This value is very important for fundamental astrophysics. This is because it’s hard to know exactly what happens when a star goes supernova, when a very large amount of mass is condensed to a very small size with high density. The more details we learn about this process in particular, the more we learn about physics in general. So while the study of super massive black holes may sound more exciting, studying the smallest of black holes may be more fundamental for our understanding of physics and matter.

So as fate would have it two days after writing my most recent blog entry, an article was published with the title “First Picture of Planet around Sun-Like Star”. In my previous blog post I mentioned how we had only indirectly observed planets around other stars and had yet to photograph one directly. Well first I must say that even before this new discovery, my statement was not entirely correct. Some people within the last year have claimed that they had photographed planets around stars. I did not mention it because the jury is still out on these pictures as to whether or not what is seen is actually an orbiting planet or perhaps just a background object.

However, even with those couple of photos floating around, this new one is slightly more interesting. Those few photos we have so far of possible planets have all been around very dim stars called red dwarfs or even dimmer brown dwarfs. This new picture is of a star that is very much like our sun. The planet observed is giant (about eight times the mass of Jupiter) and lies far out from its star (about 330 times the Earth-Sun distance). It’s large mass, or size, is one the key factors in being able to view it directly. This planet is extremely far out from its host star; for frame of reference, Neptune is our farthest planet and lies only 30 times the earth-sun distance.

The discovery was made by the Gemini North Telescope on top of Mauna Kea, which is associated with the previously mentioned Subaru Telescope. However, more studies will have to be done to prove this object is in fact orbiting the observed star, but evidence from the indirect method of detection supports the idea that this is not just a background object in the picture.

Given the distance to its star and other strange qualities such as its large mass and hot temperature (about 1500C compared to Jupiter at 110C), we may have to really start looking at our models of planet formation. Currently our theories would not predict, or allow for, such a planet to be where it is and how it is. For those who want to see the pretty picture of the planet, Google the star name 1RXS J160929.1-210524 (nice name huh?) or should be available from the Gemini observatory’s website.