Active Galactic Nuclei

Active Galactic Nuclei…. You may not know what they are, but you have to admit that they sound pretty crazy!  Many galaxies have bright centers due to stars bunched up around a super massive black hole. Active galactic nuclei (AGN) are the super bright cores of distant galaxies. AGN have supermassive black holes that are actively accreting a lot of matter. This in fall of matter creates heat, turns the region around the black hole into plasma, and emits copious amounts of light. The image above is what the active nucleus of NGC 5141 looks like in X-rays! The bright yellow center means lots of x-rays are being emitted, and therefore this region must be very hot and active. AGN are so bright that we can see ones (with good telescopes) that are as far as 12 billion light years away! When we look at AGN, we are most likely seeing light from very large and compact galaxies that existed in the beginning of the universe. There are three main types of AGN: Syefert, Blazars and Quasars. The differences lie in the type of radiation emitted.  Astronomers think that there may only be one "type" of AGN, and they look different because we are viewing them at different angles. Seyferts, Blazars and Quasars will be discussed more in future ADYK.

Image credit: Radomski, J. et al.  2003, AJ 587, 117

Kepler's First Earth Size Planets!

The Kepler space telescope has identified over 1200 potential exoplanets after only 1 year of operation. Kepler searches for exoplanets vi the transit method, i.e. watching for small dimming of stars as planets cross in front of them. Recently, members of the Kepler team confirmed the existence of a multi-planet system that contains two roughly Earth sized planets! 

Kepler 20 has 5 five, and maybe more, planets orbiting it. Kepler 20-b,c and d are 2-3 times the size of Earth, while Kepler 20-e and f are 0.87 and 1.02 times the size of Earth! All of these planets sit within 0.4 AU of the host star, closer than Mercury sits to our sun. The image above shows the five planets and their position in relation to Mercury's orbit. The sizes are roughly to scale as well. It's unlikely that these planets host life because of their close proximity to the sun. NASA just released the data to the astronomy community today, so I'll keep you updated on any future discoveries about this system!

Image Credit: David A. Aguilar (CfA) 

Comet Lovejoy

Named after the amateur astronomer who made the discovery, comet Lovejoy has been making headline news lately. The comet belongs to the Kreutz family of comets, and is most likely a small piece of the Great Comet of 1106 which broke apart in our solar system way back in the 12th century. Comet Lovejoy is on a very eccentric or oval shaped orbit which brings it very close to the sun. It's closest approach to the sun occurred a few days ago, passing only 120,000km (75,000 miles) above the sun's surface, which is extremely close!  Astronomers expected comet Lovejoy to burn up in the sun's atmosphere, but to their surprise Lovejoy survived! The comet's path was captured by both SOHO and SDO, which are satellites monitoring the sun's activity. Below is a video of a compilation of images taken by both satellites. The blue images show the comet approaching the sun towards the bottom left. The yellow images also show the comet approaching the sun, then exiting the sun's atmosphere. The final set of images have an arrow pointing out the comet, which again enters and exists the sun's atmosphere!  The fact that this comet survived means that it's probably much bigger than astronomers predicted; maybe even as larger as 0.5 miles!