November 2011
31 posts
A Galaxy Full of Surprises — NGC 3621 is bulgeless but has three central black holes
This image, from ESO’s Very Large Telescope (VLT), shows a truly remarkable galaxy known as NGC 3621. To begin with, it is a pure-disc galaxy. Like other spirals, it has a flat disc permeated by dark lanes of material and with prominent spiral arms where young stars are forming in clusters (the blue dots seen in the image). But while most spiral galaxies have a central bulge — a large group of old stars packed in a compact, spheroidal region — NGC 3621 doesn’t. In this image, it is clear that there is simply a brightening to the centre, but no actual bulge like the one in NGC 6744 (eso1118), for example.
NGC 3621 is also interesting as it is believed to have an active supermassive black hole at its centre that is engulfing matter and producing radiation. This is somewhat unusual because most of these so-called active galactic nuclei exist in galaxies with prominent bulges. In this particular case, the supermassive black hole is thought to have a relatively small mass, of around 20 000 times that of the Sun.
Another interesting feature is that there are also thought to be two smaller black holes, with masses of a few thousand times that of the Sun, near the nucleus of the galaxy. Therefore, NGC 3621 is an extremely interesting object which, despite not having a central bulge, has a system of three black holes in its central region.
This galaxy is located in the constellation of Hydra (The Sea Snake) and can be seen with a moderate-sized telescope. This image, taken using B, V, and I filters with the FORS1 instrument on the powerful VLT, shows striking detail in this odd object and also reveals a multitude of background galaxies. A number of bright foreground stars that belong to our own Milky Way are also visible.
Credit:
ESO
The Calm after the Galactic Storm
The NASA/ESA Hubble Space Telescope has caught sight of a soft, diffuse-looking galaxy that is probably the aftermath of a long-ago galactic collision. Two spiral galaxies, each perhaps much like the Milky Way, swirled together for millions of years.
In such mergers, the original galaxies are often stretched and pulled apart as they wrap around a common centre of gravity. After a few back-and-forths, this starry tempest settles down into a new, round object. The now subdued celestial body, catalogued as SDSS J162702.56+432833.9, is technically known as an elliptical galaxy.
When galaxies collide — a common event in the Universe — a fresh burst of star formation typically takes place as gas clouds mash together. At this point, the galaxy has a blue hue, but the colour does not mean it is cold: it is a result of the intense heat of newly formed blue–white stars. Those stars do not last long, and after a few billion years the reddish hues of aging smaller stars dominate an elliptical galaxy’s spectrum. Hubble has helped astronomers learn of this sequence by observing galaxy mergers at all stages of the process.
In SDSS J162702.56+432833.9, some ribbons of dust notably obscure parts of the conglomerated galaxy’s central, bluish region. Those dust lanes could be remnants of the spiral arms of the recently departed galaxies.
This picture was snapped by the Wide Field Camera of Hubble’s Advanced Camera for Surveys. The image was made through a red (F625W) and a blue (F438W) filter. The field of view is approximately 2.4 by 2.4 arcminutes.
Credit:
ESA/Hubble & NASA
Personal notice
Not trying to sound nasty or lofty here, but could random people who add me on Facebook from my blog let me know how you found me? A simple “I found you through your blog” would be nice. Can be slightly worrying to sign in and find 10 friend requests from people I don’t know, because I don’t know which are genuine people interested in my blog and which are people adding me to try and sell me stuff.
Thanks
:)
Probing a super-giant shell of gas and stars
In one of the largest known star formation regions in the Large Magellanic Cloud (LMC), a small satellite galaxy of the Milky Way, lie young and bright stellar groupings known as OB associations. One of these associations, called LH 72, was captured in this dramatic NASA/ESA Hubble Space Telescope image. It consists of a few high-mass, young stars embedded in a beautiful and dense nebula of hydrogen gas.
Much of the star formation in the LMC occurs in super-giant shells. These regions of interstellar gas are thought to have formed due to strong stellar winds and supernova explosions that cleared away much of the material around the stars creating wind-blown shells. The swept-up gas eventually cools down and fragments into smaller clouds that dot the edges of these regions and eventually collapse to form new stars.
The biggest of these shells, home to LH 72, is designated LMC4. With a diameter of about 6000 light-years, it is the largest in the Local Group of galaxies that is home to both the Milky Way and LMC. Studying gas-embedded young associations of stars like LH 72 is a way of probing the super-giant shells to understand how they formed and evolved.
This image was taken with Hubble’s Wide Field Planetary Camera 2 using five different filters in ultraviolet, visible and infrared light. The field of view is approximately 1.8 by 1.8 arcminutes.
Credit:
ESA/Hubble, NASA and D. A. Gouliermis
NASA Probe Data Show Liquid Water Evidence on Europa
› Larger image
November 16, 2011
PASADENA, Calif. — Data from a NASA planetary mission have provided scientists evidence of what appears to be a body of liquid water, equal in volume to the North American Great Lakes, beneath the icy surface of Jupiter’s moon, Europa.
The data suggest there is significant exchange between Europa’s icy shell and the ocean beneath. This information could bolster arguments that Europa’s global subsurface ocean represents a potential habitat for life elsewhere in our solar system. The findings are published in the scientific journal Nature.
“The data open up some compelling possibilities,” said Mary Voytek, director of NASA’s Astrobiology Program at agency headquarters in Washington. “However, scientists worldwide will want to take a close look at this analysis and review the data before we can fully appreciate the implication of these results.”
NASA’s Galileo spacecraft, launched by the space shuttle Atlantis in 1989 to Jupiter, produced numerous discoveries and provided scientists decades of data to analyze. Galileo studied Jupiter, which is the most massive planet in our solar system, and some of its many moons.
One of the most significant discoveries was the inference of a global saltwater ocean below the surface of Europa. This ocean is deep enough to cover the whole surface of Europa and contains more liquid water than all of Earth’s oceans combined. However, being far from the sun, the ocean surface is completely frozen. Most scientists think this ice crust is tens of miles thick.
“One opinion in the scientific community has been if the ice shell is thick, that’s bad for biology. That might mean the surface isn’t communicating with the underlying ocean,” said Britney Schmidt, lead author of the paper and postdoctoral fellow at the Institute for Geophysics, University of Texas at Austin. “Now, we see evidence that it’s a thick ice shell that can mix vigorously and new evidence for giant shallow lakes. That could make Europa and its ocean more habitable.”
Schmidt and her team focused on Galileo images of two roughly circular, bumpy features on Europa’s surface called chaos terrains. Based on similar processes seen on Earth — on ice shelves and under glaciers overlying volcanoes — they developed a four-step model to explain how the features form. The model resolves several conflicting observations. Some seemed to suggest the ice shell is thick. Others suggest it is thin.
This recent analysis shows the chaos features on Europa’s surface may be formed by mechanisms that involve significant exchange between the icy shell and the underlying lake. This provides a mechanism or model for transferring nutrients and energy between the surface and the vast global ocean already inferred to exist below the thick ice shell. This is thought to increase the potential for life there.
The study authors have good reason to believe their model is correct, based on observations of Europa from Galileo and of Earth. Still, because the inferred lakes are several miles below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell. Such a mission was rated as the second highest priority flagship mission by the National Research Council’s recent Planetary Science Decadal Survey and is being studied by NASA.
“This new understanding of processes on Europa would not have been possible without the foundation of the last 20 years of observations over Earth’s ice sheets and floating ice shelves,” said Don Blankenship, a co-author and senior research scientist at the Institute for Geophysics, where he leads airborne radar studies of the planet’s ice sheets.
Galileo was the first spacecraft to directly measure Jupiter’s atmosphere with a probe and conduct long-term observations of the Jovian system. The probe was the first to fly by an asteroid and discover the moon of an asteroid. NASA extended the mission three times to take advantage of Galileo’s unique science capabilities, and the spacecraft was put on a collision course into Jupiter’s atmosphere in September 2003 to eliminate any chance of impacting Europa.
The Galileo mission was managed by NASA’s Jet Propulsion Laboratory in Pasadena, Calif., for the agency’s Science Mission Directorate.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
For images and a video animation of the findings, visit:
http://www.jsg.utexas.edu/news/2011/11/scientists-find-evidence-for-great-lake-on-europa/ . For more information about the Galileo mission, visit: http://solarsystem.nasa.gov/galileo/ .
I’m afraid that there will be no astronomy updates again today. Will get back to it soon. I’ve not given up!
No astronomy posts or updates today (maybe tomorrow too) should be back to normal by Wednesday. :)
