Astronomy posts
- July 16, 2010
- 07:39 PM
- 956 views
Acro-tastic! (with additional GADZOOKS!)
by Emma in we are all in the gutter
I’m in need of some cheering up today, as the fun observations I wanted to make with the Herschel Space Telescope have turned out to be impossible. Luckily, this observation planning also involved a lot of procrastination, which led me to this: the Dumb Or Overly Forced Astronomical Acronyms Site (DOOFAAS). On this site astronomer [...]... Read more »
John F. Beacom, & Mark R. Vagins. (2003) GADZOOKS! Antineutrino Spectroscopy with Large Water Cerenkov Detectors. Phys.Rev.Lett. 93 (2004) 171101. arXiv: hep-ph/0309300v1
- July 16, 2010
- 10:58 AM
- 535 views
Does one size fit all when it comes to star formation?
by Kelly Oakes in Basic Space
It is widely known (among astrophysicists at least!) that disks of accumulated matter are an essential component in the formation of low mass stars. These disks form when a rotating cloud of dust and gas collapses, and they direct material from the cloud onto a protostar at the centre. This protostar keeps accreting more and [...]... Read more »
Kraus, S., Hofmann, K., Menten, K., Schertl, D., Weigelt, G., Wyrowski, F., Meilland, A., Perraut, K., Petrov, R., Robbe-Dubois, S.... (2010) A hot compact dust disk around a massive young stellar object. Nature, 466(7304), 339-342. DOI: 10.1038/nature09174
- July 15, 2010
- 12:13 PM
- 1,176 views
Thousand light year long bubble surrounds black hole in nearby galaxy
by Kelly Oakes in Basic Space
The Eddington luminosity is the exact brightness a black hole has when the outwards and inwards forces on it balance. It may seem strange to talk about the brightness of a black hole, as usually we think of them as not letting anything – including light – escape their gravitational pull, but in reality this [...]... Read more »
Pakull, M., Soria, R., & Motch, C. (2010) A 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793. Nature, 466(7303), 209-212. DOI: 10.1038/nature09168
- July 7, 2010
- 12:46 PM
- 2,802 views
Massive Early Stars And Molecular Hydrogen Cooling
by Joseph Smidt in The Eternal Universe
The big bang produced only Hydrogen and Helium with trace amounts of Lithium. (For the most part.) This is a problem for star formation because stars need to be "cool" to form and typically you need heavier elements to help the star cool off. This is why:
Gravity pulls mass together. However, as matter gets pulled together it heats up and this heat causes the matter to want to expend again.
... Read more »
Kreckel, H., Bruhns, H., Cizek, M., Glover, S., Miller, K., Urbain, X., & Savin, D. (2010) Experimental Results for H2 Formation from H- and H and Implications for First Star Formation. Science, 329(5987), 69-71. DOI: 10.1126/science.1187191
- July 6, 2010
- 01:30 AM
- 702 views
This Week in the Universe: June 29th – July 5th
by S.C. Kavassalis in The Language of Bad Physics
What have people been talking about this week in high energy physics, astrophysics, gravitation, general relativity and quantum gravity?
Sorry for the very half-assed post, it’s midnight in Mexico City and it was a long day at GR19.... Read more »
Eugenio J. Rivera, Gregory Laughlin, R. Paul Butler, Steven S. Vogt, Nader Haghighipour, & Stefano Meschiari. (2010) The Lick-Carnegie Exoplanet Survey: A Uranus-mass Fourth Planet for GJ 876 in an Extrasolar Laplace Configuration. arXiv. arXiv: 1006.4244v1
Kreckel, H., Bruhns, H., Cizek, M., Glover, S., Miller, K., Urbain, X., & Savin, D. (2010) Experimental Results for H2 Formation from H- and H and Implications for First Star Formation. Science, 329(5987), 69-71. DOI: 10.1126/science.1187191
Michel-Dansac, L., Duc, P., Bournaud, F., Cuillandre, J., Emsellem, E., Oosterloo, T., Morganti, R., Serra, P., & Ibata, R. (2010) A COLLISIONAL ORIGIN FOR THE LEO RING. The Astrophysical Journal, 717(2). DOI: 10.1088/2041-8205/717/2/L143
Eisenhardt, P., Griffith, R., Stern, D., Wright, E., Ashby, M., Brodwin, M., Brown, M., Bussmann, R., Dey, A., Ghez, A.... (2010) ULTRACOOL FIELD BROWN DWARF CANDIDATES SELECTED AT 4.5 μm. The Astronomical Journal, 139(6), 2455-2464. DOI: 10.1088/0004-6256/139/6/2455
Hüdepohl, L., Müller, B., Janka, H., Marek, A., & Raffelt, G. (2010) Neutrino Signal of Electron-Capture Supernovae from Core Collapse to Cooling. Physical Review Letters, 104(25). DOI: 10.1103/PhysRevLett.104.251101
Andersson, N. (2010) Gravity: Trying to catch the wave. Nature Physics, 6(7), 484-485. DOI: 10.1038/nphys1723
Pfrommer, C., & Jonathan Dursi, L. (2010) Detecting the orientation of magnetic fields in galaxy clusters. Nature Physics, 6(7), 520-526. DOI: 10.1038/nphys1657
Mendoza, M., Boghosian, B., Herrmann, H., & Succi, S. (2010) Fast Lattice Boltzmann Solver for Relativistic Hydrodynamics. Physical Review Letters, 105(1). DOI: 10.1103/PhysRevLett.105.014502
Luis Lehner, & Frans Pretorius. (2010) Black Strings, Low Viscosity Fluids, and Violation of Cosmic Censorship. arXiv. arXiv: 1006.5960v1
Jonathan J. Heckman, & Cumrun Vafa. (2010) An Exceptional Sector for F-theory GUTs. arXiv. arXiv: 1006.5459v1
- July 2, 2010
- 05:45 AM
- 800 views
In the news this month: a drop in eta Carinae's stellar wind
are the violent explosions of massive stars, so bright that the events can be seen in distant galaxies. But not all apparent explosions are genuine supernovae. Some fall into the category of , the sudden increase in brightness of a star without the terminal explosion. One such impostor event was the , a star which is amongst the most massive known in the Milky Way. Located 7,500 light years away in the constellation of Carina, the star is five million times more luminous than the Sun and an estimated 100 times as massive. underwent a massive but non-terminal explosion 150 years ago, allowing the close-up study of a supernova impostor. During the eruption, the star lost about ten percent of its mass, throwing off the outer layers in the surrounding nebula. Since then, the star has been enshrouded in a thick cloud of dusty debris and has been losing material at the rate of one per year in a strong stellar wind.Now, a team of researchers, led by at the University of Minnesota, have observed dramatic changes in the star's spectrum. Observations over the last decade have shown an increase in the star's magnitude, but with no major long-term changes in its spectrum, something that might be expected following an event causing a major change in brightness. carried out with the on the Hubble Space Telescope by Mehner's team in the emission lines, caused by specific elements in the star's atmosphere. According to the team, the sudden rapid decrease in the brightness of the emission lines (dropping to a third of their original strength in just ten years) suggests a decrease in the strength of the , possibly signifying a much more rapid return to the pre-explosion state than was previously anticipated. With the wind density decreasing, the nebula should begin to thin and the star itself may become visible to modern telescopes for the first time, possibly within the next decade.There are other explanations which may account for the unusual spectroscopic developments, including a change in the latitude dependence of the wind, but the complicated nature of the surrounding nebula and the difficulties constructing accurate models make an accurate assessment problematic.This blog post is a news story from the , aired in the edition.... Read more »
Mehner, A., Davidson, K., Humphreys, R., Martin, J., Ishibashi, K., Ferland, G., & Walborn, N. (2010) A SEA CHANGE IN ETA CARINAE . The Astrophysical Journal, 717(1). DOI: 10.1088/2041-8205/717/1/L22
- July 1, 2010
- 08:05 AM
- 549 views
Eclipse in The Odyssey: Science Meets Mythology
by agoldstein in WiSci
In The Odyssey, the oracle Theoclymenus delivers a speech portending the suitors’ deaths at the hand of Odysseus. However, some scholars believe that Homer, the poem’s author, was also describing a total solar eclipse.... Read more »
Baikouzis, C., & Magnasco, M. (2008) From the Cover: Is an eclipse described in the Odyssey?. Proceedings of the National Academy of Sciences, 105(26), 8823-8828. DOI: 10.1073/pnas.0803317105
- June 28, 2010
- 06:18 PM
- 776 views
This Week in the Universe: June 22nd – June 28th
by S.C. Kavassalis in The Language of Bad Physics
What have people been talking about this week in high energy physics, astrophysics, gravitation, general relativity and quantum gravity, and a little bit of quantum mechanics?... Read more »
Lyne, A., Hobbs, G., Kramer, M., Stairs, I., & Stappers, B. (2010) Switched Magnetospheric Regulation of Pulsar Spin-Down. Science. DOI: 10.1126/science.1186683
H. Rampadarath, M. A. Garrett, G. I. G. Józsa, T. Muxlow, T. A. Oosterloo, Z. Paragi1, R. Beswick, H. van Arkel, W. C. Keel, & K. Schawinski. (2010) Hanny's Voorwerp: Evidence of AGN activity and a nuclear starburst in the central regions of IC 2497. arXiv. arXiv: 1006.4096v1
Norbert Przybilla, Alfred Tillich, Ulrich Heber, & Ralf-Dieter Scholz. (2010) Weighing the Galactic dark matter halo: a lower mass limit from the fastest halo star known. arXiv. arXiv: 1005.5026v1
Andresen, G., Bertsche, W., Bowe, P., Bray, C., Butler, E., Cesar, C., Chapman, S., Charlton, M., Fajans, J., & Fujiwara, M. (2010) Antihydrogen formation dynamics in a multipolar neutral anti-atom trap. Physics Letters B, 685(2-3), 141-145. DOI: 10.1016/j.physletb.2010.01.066
Shaun A. Thomas, Filipe B. Abdalla, & Ofer Lahav. (2010) Upper bound of 0.28 eV on neutrino masses from the largest photometric redshift survey. |Physical Review Letters. info:/
The CDMS II Collaboration. (2010) Dark Matter Search Results from the CDMS II Experiment. Science, 327(5973), 1619-1621. DOI: 10.1126/science.1186112
Tarun Biswas. (2010) Through the Black Hole -- On Not Breaking Time Reversal Symmetry. arXiv. arXiv: 1006.4185v1
A. Garrett Lisi. (2010) An Explicit Embedding of Gravity and the Standard Model in E8. arXiv. arXiv: 1006.4908v1
Ian D. Leroux, Monika H. Schleier-Smith, & Vladan Vuletić. (2010) Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock. Physical Review Letters. info:/10.1103/PhysRevLett.104.250801
Schultze, M., Fiess, M., Karpowicz, N., Gagnon, J., Korbman, M., Hofstetter, M., Neppl, S., Cavalieri, A., Komninos, Y., Mercouris, T.... (2010) Delay in Photoemission. Science, 328(5986), 1658-1662. DOI: 10.1126/science.1189401
- June 25, 2010
- 07:42 PM
- 1,353 views
Night of the Living Dead Stars
by Professor Astronomy in Professor Astronomy
Image Credit: NASA / Spitzer / JPL-Caltech
White dwarfs, the slowly cooling remains of stars that have completed their life cycles, often seem to be the zombies of the night sky, devouring anything that happens to stray within their grasp. In an article that will be appearing in an upcoming issue of the Astrophysical Journal, astronomers Patrick Dufour, Mukremin Kilic and collaborators discuss a recently-discovered white dwarf that seems to have devoured a dwarf planet. Its name: "SDSS J073842.56+183509.6" (its nickname: 5877352363341268816. Seriously.)
White dwarfs have so much matter squeezed into such a little size that their pull of gravity is very strong. If you were to try and stand on the surface of the white dwarf remains of the sun, you would weigh one hundred thousand times more than you do now. So, if you weigh 150 pounds, on a white dwarf you would weigh 15 million pounds. Ouch.
That gravity is strong enough that the lightest element in a white dwarf's atmosphere will float to the top. The lightest element in the universe is hydrogen, and most white dwarfs have atmospheres of pure hydrogen. If you were to dump a heavy element, like iron, into a hydrogen-atmosphere white dwarf, it would disappear in a matter of weeks. That's fast in a science like astronomy when a million years is the blink of an eye! Take the sun, for instance. The sun has been around for four billion years, and yet its surface still has almost as much iron as it did when it formed.
Some white dwarfs have helium atmospheres (the second lightest element in the universe). In these white dwarfs, iron might not sink out of sight for a thousand years. Again, that's still very short in astronomy. The take-away point here is that if you see any element heavier than hydrogen or helium in the atmosphere of a white dwarf, it just got there within the last thousand years.
Okay, back to the white dwarf studied by Patrick, Mukremin and their collaborators. This white dwarf has a helium atmosphere, but all kinds of other heavier elements are also seen, including oxygen, magnesium, silicon, calcium, and iron. Remember, this means that these elements just recently landed on the surface of the white dwarf. These elements are similar to the composition of asteroids and comets, so when we find them in the atmosphere of a white dwarf, we assume that an asteroid or comet recently came too close to the white dwarf, was shredded and devoured like in the picture above.
By carefully analyzing the spectrum of the white dwarf, Dufour's team was able to determine that the white dwarf is about 90% the mass of the sun, meaning the original star was about 4 or 5 times the mass of the sun. With some more careful modeling, they were even able to add up the estimated total amount of rock swallowed by the white dwarf. The result was big: the asteroid eaten by the white dwarf was the size of Ceres, the largest asteroid in the Solar System. Ceres is so much bigger than the typical asteroid that it is now officially a "dwarf planet", the same designation that former planet Pluto was awarded as a consolation prize. (Pluto has about 10 times the mass of Ceres.) This is also at least 10 times more asteroidal material than any other known white dwarf has in its atmosphere. And remember, this amount of material has been swallowed in recent past!
Even better, it's possible to guess at the past history of the recently-deceased dwarf planet. The white dwarf shows evidence for a little hydrogen, but not much. This means that the doomed planet had little water or ice, just like asteroids in our own Solar System (and unlike comets). Of course, the red giant star that became a white dwarf would likely have evaporated any water ice, so it is hard to know whether the planet may have had water before its parent star died.
There is also some evidence in infrared light that the white dwarf has not swallowed all of the asteroid yet. It's hard to tell exactly what fraction of the asteroid material remains around the white dwarf. It could be that the white dwarf has already swallowed all but one percent of the asteroid, or it could be that half the shredded asteroid remains to be swallowed.
So, why is this surprising? After all, we see comets falling into the sun every few days.
When a star dies, it swells up into a red giant star. The Sun will expand in size about 80 times, reaching out to the orbit of the Earth and swallowing any planet, asteroid or comet inside of that distance. A star four times the mass of the sun, like the progenitor of the white dwarf in this study, will swell up twice as big as that -- beyond the orbit of Mars and to the inner region of the asteroid belt.
Red giant stars then shed their outer layers, with the core of the star shrinking to an orb about the size of the Earth. In order for an asteroid to get shredded and swallowed by the white dwarf, it has to come within about a million miles of the white dwarf star. But the red giant star cleared out everything within about 200 million miles of the star. Somehow the asteroid has to live further from its parent star than 200 million miles for almost a billion years, and then somehow get flung in very close to the white dwarf. In other words, the white dwarf needs and accomplice.
In order for the doomed asteroid to get flung in close to the white dwarf, the hidden accomplice has to be bigger than the asteroid. So we know that there must something at least the size of another dwarf planet around this white dwarf. But the bigger the accomplice, the easier it is to throw the asteroid in toward the white dwarf.
In our Solar System, Jupiter is a bully. Its gravity has been constantly tossing asteroids and comets around, sometimes flinging them in toward the sun, often flinging them out of the Solar System and into the icy depths of deep space. And Jupiter is far enough away from the Sun to survive the Sun's death throes. Therefore, I would not be surprised if there is a Jupiter-sized planet lurking around the white dwarf, and this big planet is responsible for sending the dwarf planet to its doom.
This sounds like the beginning of a bad science fiction movie. A zombie star (dead, but yet alive) being fed the occasional dwarf planet by an unseen accomplice. An international team of astronomers on Earth have uncovered this sinister plot. Can they save other innocent dwarf planets from this horrible fate? Stay tuned...
P. Dufour, M. Kilic, G. Fontaine, P. Bergeron, F. -R. Lachapelle, S. J. Kleinman, & S. K. Leggett (2010). "The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet" Accepted for publication in The Astrophysical Journal arXiv: 1006.3710v1... Read more »
P. Dufour, M. Kilic, G. Fontaine, P. Bergeron, F. -R. Lachapelle, S. J. Kleinman, & S. K. Leggett. (2010) The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet. The Astrophysical Journal. arXiv: 1006.3710v1
- June 21, 2010
- 10:30 PM
- 872 views
This Week in the Universe: June 15th – June 21st, 2010
by S.C. Kavassalis in The Language of Bad Physics
What have people been talking about this week in high energy physics, astrophysics, gravitation, general relativity and quantum gravity?... Read more »
T. van Zoest, N. Gaaloul, Y. Singh, H. Ahlers, W. Herr, S. T. Seidel, W. Ertmer, E. Rasel, M. Eckart, E. Kajari, S. Arnold, G. Nandi, W. P. Schleich, R. Walser, A. Vogel, K. Sengstock, K. Bongs, W. Lewoczko-Adamczyk, M. Schiemangk, T. Schuldt, A. Peters, . (2010) Bose-Einstein Condensation in Microgravity. Science , 328(5985), 1540-1543. info:/10.1126/science.1189164
Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, & Nolan R. Walborn. (2010) A Sea Change in Eta Carinae. arXiv. arXiv: 1004.3529v3
Bogdan A. Dobrescu, Patrick J. Fox, & Adam Martin. (2010) CP violation in B_s mixing from heavy Higgs exchange. arXiv. arXiv: 1005.4238v2
- June 14, 2010
- 03:44 PM
- 848 views
This Week in the Universe: June 8th – June 14th, 2010
by S.C. Kavassalis in The Language of Bad Physics
What have people been talking about this week in high energy physics, astrophysics, gravitation, general relativity and quantum gravity?... Read more »
Christophe Ringeval, Teruaki Suyama, Tomo Takahashi, Masahide Yamaguchi, & Shuichiro Yokoyama. (2010) Dark energy from primordial inflationary quantum fluctuations. arXiv. arXiv: 1006.0368v1
U. Sawangwit, & T. Shanks. (2009) Beam profile sensitivity of the WMAP CMB power spectrum. arXiv. arXiv: 0912.0524v2
Feldman, D., Liu, Z., Nath, P., & Peim, G. (2010) Multicomponent dark matter in supersymmetric hidden sector extensions. Physical Review D, 81(9). DOI: 10.1103/PhysRevD.81.095017
K. S. Cheng, Yun-Wei Yu, & T. Harko. (2010) High Redshift Gamma-Ray Bursts: Observational Signatures of Superconducting Cosmic Strings?. arXiv. arXiv: 1005.3427v2
- June 9, 2010
- 04:01 AM
- 1,358 views
the media finds life on titan. sort of…
by Greg Fish in weird things
Around the web, headlines are buzzing about alleged evidence for life on Saturn’s biggest moon Titan, citing a paper which noted a suspicious lack of hydrogen build-up in the lower atmosphere and listing among many a mundane explanation, the possibility of methane-based life. Now, while on this blog I discussed that it’s not impossible to [...]... Read more »
- June 7, 2010
- 03:45 PM
- 799 views
This Week in the Universe: June 1st – June 7th, 2010
by S.C. Kavassalis in The Language of Bad Physics
This is the first post in a new weekly series looking at what is making the (science) news in high energy physics, astrophysics, gravitation, general relativity and quantum gravity, and, perhaps more importantly, do the stories mean what we think they mean.
What have people been talking about this week?... Read more »
Rochau, B., Brandner, W., Stolte, A., Gennaro, M., Gouliermis, D., Da Rio, N., Dzyurkevich, N., & Henning, T. (2010) INTERNAL DYNAMICS AND MEMBERSHIP OF THE NGC 3603 YOUNG CLUSTER FROM MICROARCSECOND ASTROMETRY. The Astrophysical Journal, 716(1). DOI: 10.1088/2041-8205/716/1/L90
Evans, C., Walborn, N., Crowther, P., Hénault-Brunet, V., Massa, D., Taylor, W., Howarth, I., Sana, H., Lennon, D., & van Loon, J. (2010) A MASSIVE RUNAWAY STAR FROM 30 DORADUS. The Astrophysical Journal, 715(2). DOI: 10.1088/2041-8205/715/2/L74
D. Batcheldor, A. Robinson, D. J. Axon, E. S. Perlman, & D. Merritt. (2010) A Displaced Supermassive Black Hole in M87. arXiv. arXiv: 1005.2173v1
Hammer, N., Janka, H., & Müller, E. (2010) THREE-DIMENSIONAL SIMULATIONS OF MIXING INSTABILITIES IN SUPERNOVA EXPLOSIONS. The Astrophysical Journal, 714(2), 1371-1385. DOI: 10.1088/0004-637X/714/2/1371
Garofalo, D., Evans, D., & Sambruna, R. (2010) The evolution of radio-loud active galactic nuclei as a function of black hole spin. Monthly Notices of the Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2010.16797.x
Meng Su, Tracy R. Slatyer, & Douglas P. Finkbeiner. (2010) Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?. arXiv. arXiv: 1005.5480v1
Kanekar, N., Chengalur, J., & Ghosh, T. (2010) PROBING FUNDAMENTAL CONSTANT EVOLUTION WITH REDSHIFTED CONJUGATE-SATELLITE OH LINES. The Astrophysical Journal, 716(1). DOI: 10.1088/2041-8205/716/1/L23
The D0 Collaboration, & V. M. Abazov. (2010) Evidence for an anomalous like-sign dimuon charge asymmetry. arXiv. arXiv: 1005.2757v1
Eder Izaguirre, Michael Manhart, & Jay G. Wacker. (2010) Bigger, Better, Faster, More at the LHC. arXiv. arXiv: 1003.3886v1
Gale, C. (2010) Taking the temperature of extreme matter. Physics. DOI: 10.1103/Physics.3.28
Kribs, G., Roy, T., Terning, J., & Zurek, K. (2010) Quirky composite dark matter. Physical Review D, 81(9). DOI: 10.1103/PhysRevD.81.095001
- June 7, 2010
- 04:20 AM
- 878 views
In the news this month... Hubble spots a planet-eating star
Most of the discovered so far are in the class known as "", large gas giants orbiting close to their parent stars, since many of the search techniques used are most sensitive to this type of planet. Usually these planets are located close enough to their parent star that they orbit in just a few days, but a team that is orbiting so close to its parent star that it is actually being disrupted.The planet, known as WASP-12b, is located in the constellation of Auriga and was discovered in the , or WASP, operated by a consortium of eight academic institutions. WASP consists of two robotic observatories, one located at La Palma in the Canary Islands, the other at the South African Astronomical Observatory at Sutherland in South Africa, both scanning the sky for the tiny dimming effects caused when a planet transits in front of a star. This particular planet orbits its parent star, a yellow dwarf known as WASP-12, in just 1.1 Earth days, and shows evidence of an atmosphere which extends far further from the planet than would be expected for a body of this size.Previous observations have shown that at least one other exoplanet displays evidence of such an extended atmosphere, and two different mechanisms have been suggested: either heating from the parent star, or an interaction with the stellar wind. This new planet was first discovered by the WASP survey in 2008, and was predicted to be physically distorted by its proximity to the host star. These new observations, made with the on the Hubble Space Telescope and during May, have verified the prediction. WASP-12b is so close to the star that the tidal forces exerted on it have heated and deformed it far from the normal almost-spherical planetary shape, so far in fact that the internal heating has caused the atmosphere to expand far enough that it is being dragged off onto the surface of the star.Absorption from elements such as , , and was expected in the atmosphere of the star, and the increase in absorption during the transit allowed the astronomers to calculate how common these elements are in the planet's atmosphere. The research, led by Luca Fossati at the in the UK, examined the ultra violet spectrum of the planet's atmosphere and found a much greater abundance of than expected from models of planetary atmospheres. The suggested reason for this unexpected result is that the high amount of incident radiation due to the close proximity of the star, together with tidal effects, cause a large amount of mixing within the atmosphere, pulling heavy elements higher in the atmosphere than they would normally be found. The heating also causes the atmosphere to expand, overflowing what is known as the , the point beyond which particles escape the gravitational pull of the planet and are lost to the surrounding space.From the evidence provided by their ultra-violet observations, the researchers conclude that the planet is probably undergoing by its host star, and the material lost from the atmosphere is forming a diffuse ring around the star along the planet's orbit. While few examples of such systems are currently known, further observations and detailed modelling will help to determine exactly what is going on in these peculiar atmospheres.This blog post is a news story from the , aired in the edition.... Read more »
Fossati, L., Haswell, C., Froning, C., Hebb, L., Holmes, S., Kolb, U., Helling, C., Carter, A., Wheatley, P., Cameron, A.... (2010) METALS IN THE EXOSPHERE OF THE HIGHLY IRRADIATED PLANET WASP-12b. The Astrophysical Journal, 714(2). DOI: 10.1088/2041-8205/714/2/L222
- June 7, 2010
- 04:00 AM
- 971 views
In the news this month... runaway star in 30 Doradus
One of the most spectacular examples of a star formation region in the nearby universe is , also known as the , located in the Large Magellanic Cloud. This region is a giant stellar nursery, similar to the , but much larger, containing many clusters of recently formed young, hot stars. Some of the young stars in the nebula are many tens of times more massive than the Sun, making them some of the most massive stars known. New observations, on May 5th, show that one particular star is travelling away from the nebula at high velocity.The star, known as 30 Dor 016, was first spotted in 2006 when it was observed by the at Siding Spring Observatory in Australia. It was found to be an exceptionally hot, massive blue-white star, located relatively far from any cluster in which such stars are usually found. More recent observations made during the calibration of the , installed on the Hubble Space Telescope during servicing mission four in May 2009, showed that the star had an unusually fast stellar wind, almost 3500 km/s, one of the most powerful ever detected and a strong indication that the star is incredibly massive - it is estimated to be roughly 90 times the mass of the Sun. Its size means that it must be young - stars this large only live for a few million years before exploding as core collapse supernovae.Archive images taken by Hubble's in 1995, show that the star is at one end of an egg-shaped cavity in the surrounding interstellar gas which points towards 30 Doradus, in the direction of a cluster of massive stars known as R136, the likely birthplace of the star. Further observations, made with the in Chile, have shown that the star's velocity is more than 400,000 kilometres an hour, a speed that would get you from the Earth to the Moon in an hour. The measured velocity could have been due to orbital motion if the star had a companion, but the VLT observations show that it is a single massive star, and the velocity is due to motion away from the nebula.Stars can end up with such high velocities as a result of nearby explosions. In the case of 016 however, this is unlikely since the stars in 30 Doradus are still too young to have exploded as supernovae. The more likely explanation, , led by Chris Evans at the in Edinburgh, is that it was ejected from the cluster by dynamical interactions with other massive stars, one of the clearest examples yet of such a process.This blog post is a news story from the , aired in the edition.... Read more »
Evans, C., Walborn, N., Crowther, P., Hénault-Brunet, V., Massa, D., Taylor, W., Howarth, I., Sana, H., Lennon, D., & van Loon, J. (2010) A MASSIVE RUNAWAY STAR FROM 30 DORADUS. The Astrophysical Journal, 715(2). DOI: 10.1088/2041-8205/715/2/L74
- June 7, 2010
- 03:45 AM
- 629 views
In the news this month... a possible new class of supernova
Most supernovae are classified as one of two different types of explosion: single massive short-lived stars that explode when their cores run out of fuel at the end of their lives and undergo gravitational collapse, and old evolved white dwarfs in binary systems which accrete hydrogen from a companion star before exploding catastrophically.; are generally seen only in regions of ongoing star formation since, by stellar standards, their supergiant progenitors do not live for very long. In contrast, in binary systems are produced by old, evolved stars and so are seen in all galaxy types, even those which show no signs of recent star formation. However, in the May 20th issue of the journal Nature, two groups of astronomers with characteristics that do not fit into existing categories of supernovae, and come to very different conclusions about their progenitors.The first event, , was observed in the edge-on spiral galaxy in 2005 and was initially classified as a type Ib (core collapse) supernova based on the chemical elements detected in its optical spectrum soon after explosion. Located in the , rather than the disk of the galaxy, the surrounding environment is composed of an old stellar population with no recent star formation, an unlikely location for a core collapse supernova. While some of its properties show similarities to type Ia explosions, the lightcurve shows a much faster decline than is expected for the thermonuclear explosion of a white dwarf. The mass ejected in the explosion, less than a third of a solar mass, is also low for this class of supernova, and analysis of the spectra showed significant differences from what is expected from either explosion mechanism. lead Dr Perets' team to conclude that the progenitor was something unusual, likely to be a helium-rich low mass star, probably a helium-accreting white dwarf, making 2005E the first example of a new class of supernova.However, 2005E is not the only supernova with these unusual characteristics; several other calcium-rich, subluminous supernovae, spectroscopically classified as type Ib/c events, have also been observed. One such event is SN 2005cz, in the same issue of Nature. While 2005cz shares many properties with 2005E, Kawabata's team reaches a different conclusion on the cause of the explosion. According to their study, supernovae in this class are more likely to originate via the core collapse mechanism, but from stars with masses at the lower end of the range of those that explode. Unlike 2005E, SN2005cz is located in an . These galaxies are generally made up of old stellar populations, but NGC4589 has a relatively young stellar population (for an elliptical galaxy) so the explosion of a star by core collapse is not ruled out.Since most supernova searches are more likely to detect bright events, the number of faint 2005E-like events currently known is small. More sensitive surveys are planned, however, and these should result in many more examples and further insights into this non-standard class of supernova.This blog post is a news story from the , aired in the edition.... Read more »
Perets, H., Gal-Yam, A., Mazzali, P., Arnett, D., Kagan, D., Filippenko, A., Li, W., Arcavi, I., Cenko, S., Fox, D.... (2010) A faint type of supernova from a white dwarf with a helium-rich companion. Nature, 465(7296), 322-325. DOI: 10.1038/nature09056
Kawabata, K., Maeda, K., Nomoto, K., Taubenberger, S., Tanaka, M., Deng, J., Pian, E., Hattori, T., & Itagaki, K. (2010) A massive star origin for an unusual helium-rich supernova in an elliptical galaxy. Nature, 465(7296), 326-328. DOI: 10.1038/nature09055
- May 31, 2010
- 02:09 PM
- 1,195 views
In the news this month... volcanoes on Venus
Closer to home, the planet Venus shows large amounts of evidence of volcanic activity. Despite being shrouded under a thick layer of cloud, spacecraft have been able to map the surface of our nearest neighbour using radar, leading to the realisation that much of the planet's surface is comparatively young, suggesting that at some point in the recent past the planet underwent a complete resurfacing. However the question remains whether Venus is currently a geologically active planet.... Read more »
Smrekar, S., Stofan, E., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., Piccioni, G., & Drossart, P. (2010) Recent Hotspot Volcanism on Venus from VIRTIS Emissivity Data. Science, 328(5978), 605-608. DOI: 10.1126/science.1186785
- May 31, 2010
- 09:49 AM
- 630 views
In the news this month... the strange atmosphere of GJ 436b
Most known extrasolar planets are massive gas giants orbiting close to their parent stars. If one of these planets happens to pass directly between us and its parent star during its orbit, then sensitive spectroscopy can be used to determine the chemical make-up of its atmosphere. Models of such atmospheres predict which gases should be present and in what relative abundances, based on physical conditions such as the temperature. Recent infra red observations carried out with the have provided the first details of the atmospheric composition of a so-called hot Neptune.The planet, known as , orbits an M-type dwarf star in the constellation of Leo. It is similar to Neptune in size, but orbits its parent star in just 2.6 days. Previous observations of the planet showed that its surface temperature was estimated to be 712 K, higher than predicted due to stellar heating alone, and the new observations () suggest that its atmosphere may not be in equilibrium. The team, led by Kevin Stevenson at the University of Central Florida, observed the planet's day side as it passed around the far side of the star and examined the infra red spectrum for various chemical signatures. What they found was a high abundance of carbon monoxide and a deficiency of methane compared to predictions from atmospheric models at this temperature for an atmosphere thought to be dominated by hydrogen. In an atmosphere such as this, methane (one carbon atom and four hydrogen atoms) should be the main carbon-bearing molecule, but the observations show the actual abundance is less than that predicted by a factor of seven thousand. The large amount of absorption due to carbon monoxide is also unexpected, the results suggesting that the atmosphere may not be in thermochemical equilibrium.One alternative explanation considered by the authors is that the atmosphere may not be dominated by hydrogen, but this is unlikely given the dominance of hydrogen in planet forming disks. Another possibility is that vertical mixing within the atmosphere may dredge up carbon monoxide from lower, hotter parts of the atmosphere, although the authors point out that, in order to explain the observed abundances, the amount of mixing would have to be large. These new data will provide useful information for future atmospheric modeling.This blog post is a news story from the , aired in the edition.... Read more »
Stevenson, K., Harrington, J., Nymeyer, S., Madhusudhan, N., Seager, S., Bowman, W., Hardy, R., Deming, D., Rauscher, E., & Lust, N. (2010) Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b. Nature, 464(7292), 1161-1164. DOI: 10.1038/nature09013
- May 31, 2010
- 08:19 AM
- 648 views
In the news this month... the nature of the eclipsing binary system epsilon Aurigae
Many stars vary in brightness, sometimes due to changes within the star itself such as novae or Cepheid variables, others because of external factors. One is , an F-type supergiant in the constellation of Auriga, located at an estimated distance of 625 parsecs (2,100 light years). Since its variable nature was discovered in the 1820s, the star has been seen to fade in brightness every 27.1 years. During these eighteen-month-long eclipses, the brightness of the star fades to around 50 per cent of its normal magnitude. While the variability of the system has been well-studied, the exact physical nature of the eclipsing companion is less certain as it has remained undetected, and many models have been put forward to explain the unusual nature of the system. Observations of epsion Aurigae show that the star and its darker companion have a similar mass which, until recently, was thought to be around 15 times the mass of the Sun. have shown that the supergiant star has a much lower mass of between two and three solar masses, and that the companion may be a single B5V-type star embedded within a disk of opaque material.Now, using the CHARA interferometer, an array of infrared telescopes located on Mount Wilson in California, a team led by Brian Kloppenborg from the University of Denver have . This is the first time a spatially resolved observation of an eclipsing binary has been made. Their observations show that the eclipsing object is an opaque disk of dust, tilted to our line of sight by an estimated 84 degrees. From the motion of the disk between two observations carried out in November and December 2009, the team infer that the companion object is more massive than the visible F-type supergiant. Assuming the B-type star within the disk has a typical mass of 5.9 solar masses, the researchers calculate a mass of 3.6 solar masses for the F-type supergiant. They also calculate that if the disk is composed entirely of dust, then its mass is less than 10 per cent of the Earth's.While the nature of the disk is now clearer, there are still several unanswered questions which remain. The model that best fits the data is of a geometrically thin disk tilted to our line of sight, rather than a thick disk seen edge on. However, the fact that it is opaque suggests that its nature is more like a debris disk than a dusty accretion disk around a young stellar object. The tilted disk model also predicts a central hole which should cause a mid-eclipse brightening of the F-type star. Observers the world-over will continue to monitor the system during the eclipse, and the data should help build up a profile of the disk and constrain the evolutionary history of the system.This blog post is a news story from the , aired in the edition.... Read more »
Kloppenborg, B., Stencel, R., Monnier, J., Schaefer, G., Zhao, M., Baron, F., McAlister, H., ten Brummelaar, T., Che, X., Farrington, C.... (2010) Infrared images of the transiting disk in the ε Aurigae system. Nature, 464(7290), 870-872. DOI: 10.1038/nature08968
- May 27, 2010
- 04:30 AM
- 810 views
Water, Mars & Herschel (everyone else can, why can’t we?)
by Emma in we are all in the gutter
The first set of results from the Herschel Space Telescope have been flooding out over the past couple of weeks*, so it’s about time they got a mention here. Rather than rehashing one of the many press releases, I thought I’d focus on an interesting result that I doubt will get much attention – the [...]... Read more »
B. M. Swinyard, P. Hartogh, S. Sidher, T. Fulton, E. Lellouch, C. Jarchow, M. J. Griffin, R. Moreno, H. Sagawa, G. Portyankina.... (2010) The Herschel-SPIRE submillimetre spectrum of Mars. to appear in the Herschel Special Issue of Astronomy . arXiv: 1005.4579v1
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