Date: November 28th, 2012
Title: Monthly News Roundup – A Month for Misfits
Podcaster: Morgan Rehnberg
Description: Orphan planets, baby supermassive black holes, and dwarf planets headline in November. A nearby exoplanet poses for a portrait. What has NASA found?
Bio: Morgan Rehnberg is a graduate student at the University of Colorado – Boulder, where he studies the rings of Saturn under the direction of Dr. Larry Esposito. Morgan received his B.S. in Physics from Beloit College and is the developer of the PhAst software package for the viewing and manipulating of astronomical images
Today’s Sponsor: “This episode of 365 days of astronomy was sponsored by Clear Skies Observing Guides, a Modern Day Celestial Handbook. www.clearskies.eu ..Clear skies observing guides, or CSOG, is a new concept in visual amateur astronomy. The observing guides contain thousands of objects to observe through amateur telescopes, with matching tours for GOTO telescopes and matching AstroPlanner plan-files. CSOG allows you to target deep-sky objects and carbon stars you never observed before, night after night. Wishing astronomers around the world: Clear skies..! ”
You’re listening to the 365 Days of Astronomy podcast for November 28th, 2012. I’m Morgan Rehnberg, and this is the Monthly News Roundup. This episode was recorded on November 25th from Boulder, Colorado.
Let’s start this month with the curious case of an orphan planet. Orphans, sometimes called rogue planets, are planet-sized bodies which are floating through space but not orbiting a star. The same International Astronomical Union guidelines that stripped Pluto of its planet-hood also require that planets be directly orbiting a star, so there is a bit of ambiguity here. Most astronomers still refer to orphans as planets, however, because they were most likely born in orbit around a star. Some subsequent interaction with a fellow planet or another star flung these bodies out of their solar systems and into lonely journeys through space.
This most recent orphan carries the tongue-twisting name of CFBDSIR2149-0403. Although it was first noticed several years ago, recent observations have pinned down its location to a star cluster about 100 lightyears from Earth. The planet appears to be part of the AB Doradus moving group, a cluster of young stars which formed between 50 and 120 million years ago. About the size of Jupiter but several times more massive, this body’s age was vital to deciding whether it is a planet or a so-called brown dwarf. Brown dwarfs are bodies just barely too small to become a star but larger than a typical planet.
This rogue planet may not have to wander forever. If it approaches another star closely, it may get trapped by that star’s gravity and enter orbit once again.
Next up is another misfit of the astronomical world. Astronomers using NASA’s Chandra X-ray telescope announced recently the discovery of the smallest-ever supermassive black hole. Supermassive black holes live at the center of galaxies and provide the mass around which all the stars of the galaxy orbit. They are believed to be present in most, if not all, galaxies in the Universe, including our own Milky Way.
This black hole was found in the center of galaxy NGC 4178, about 55 million lightyears away. It’s unique in two distinct ways. Its mass, about 200,000 times larger than that of the Sun, is downright diminutive compared to those in other galaxies. The black hole at the center of the Milky Way, for example, is just over 4 million solar masses, while larger examples can have masses hundreds of millions or even tens of billions times larger than the Sun. What makes this black hole so much smaller? It may have to do with the other unusual feature of this galaxy. Unlike most galaxies, NGC 4178 lacks a central bulge of stars extending up from the flat disk of the galaxy. Theoretical work had suggested that such a bulge was vital for the formation of a supermassive black hole. The stars in the bulge provided a feeding mechanism which allowed the black hole to grow to such incredible proportions. The lack of such a source may account for the small size of this particular specimen.
Evidence suggests that the black hole is still feeding on nearby stars, however, so perhaps its status as the tiniest member of the largest class of compact objects will someday be passed on.
Let’s swing back through our own solar system and take a look at the dwarf planet Makemake. First discovered in 2005, Makemake is the largest known Kuiper Belt object, with a radius about two-thirds that of Pluto. Orbiting at 53 AU, it’s super-cold surface is likely covered with ices of gasses such as methane and nitrogen. What was less clear was whether Makemake held on to any sort of atmosphere. It’s larger sibling Pluto clings to an atmosphere about a million times thinner than Earth’s, a phenomenon the upcoming New Horizons spacecraft will investigate.
A recent occultation by Makemake, described this month in the journal Nature, reveals no observable atmosphere. At most, the object’s atmosphere is a hundred time thinner than that of Pluto, and thus currently undetectable. An occultation occurs when a body of interest, such as Makemake, passes in front of a background star. Astronomers measure the light from the star and watch it change in brightness and color as it passes behind the object. These changes can then be converted into quantities such as the shape and size of an object.
Like most Kuiper Belt objects, Makemake’s orbit is significantly eccentric. This means that at times it is much closer to the Sun than it is today. During these periods, the dwarf planet could form a larger, more easily-detectable atmosphere.
Another far-out body also had its first close-up this month. Astronomers revealed the first-ever pictures of the exoplanet Kappa Andromedae b. Known as Kap And b for short, it joins the limited ranks of planets that have been directly imaged. It is especially interesting because it orbits its host star at about the same distance that Neptune orbits the Sun. Because of technical limitations, most previously-imaged exoplanets were much farther from their stars. It’s close-in nature increases the likelihood that it formed in a method similar to the planets in our solar system. Planet formation seems to be strongly linked to distance from the star, although modern planetary formation models are still in their infancy.
Directly imaging an exoplanet is tricky business. The central star is usually about a billion times brighter than planets that orbit it. This light must be blocked out, which can sometimes block out close-in planets as well. Even if the planet is not blocked out, its extreme dimness means that only planets around the closest stars can be imaged. Kap And b, at about 170 lightyears away, is right in our cosmic neighborhood. If an image can be obtained the planet will appear just like a star, a single faint dot in the picture. Nevertheless, imaging is a promising field of research going forward. As larger telescopes and better detectors come online, more and more planets will become directly visible.
We finish up this month with a teaser. Last week the chief scientist for the Curiosity rover, John Grotzinger, announced that the Martian rover had found something ‘big’. The discovery was made by the rover’s chemical sample analysis instrument. Scientists at NASA will be taking several weeks to confirm their findings before releasing them publicly, but, tantalizingly, the sample analysis instrument is designed to look for organic compounds – an important factor in the search for life. Until next month, however, there’s nothing to do but wait.
Thanks for listening to this episode of the Monthly News Roundup. As always, I appreciate your comments and corrections. You can email me at Morgan.Rehnberg@colorado.edu. I’ll see you next month!
End of podcast:
365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.