I can’t begin today’s entry, which deals with an unusual planet indeed, without first mentioning the passing of Allan Sandage, a man whose work I have admired for my entire adult life. A protegé of Edwin Hubble, Sandage would refine the latter’s findings, re-examining Hubble’s distance measurements to galaxies like Andromeda and helping us fine-tune our estimates of Hubble’s Constant, a measure of the expansion of the universe. In fact, our current estimate, 71 kilometres per second per megaparsec, is only slight off Sandage’s 1958 result. A final paper, on RR Lyrae variable stars, appeared as recently as June, one of 500 papers the astronomer wrote. Astronomy Now has a fine obituary of Sandage, who died at the age of 84.
Looking Back from the Future
Maybe it’s the death of Sandage that has me in a retrospective mood as I tackle a most unusual exoplanet story. All morning I’ve been remembering a passage from H.G. Wells’ The Time Machine in which the time traveler has found his way to the remote future and looks out upon a desolate world populated by huge, crab-like creatures. On the beach he has the view of the swollen Sun, bloated and entering what we would now call its red giant phase. Wells writes:
I moved on a hundred years, and there was the same red sun–a little larger, a little duller–the same dying sea, the same chill air, and the same crowd of earthy crustacea creeping in and out among the green weed and the red rocks. And in the westward sky, I saw a curved pale line like a vast new moon.
‘So I travelled, stopping ever and again, in great strides of a thousand years or more, drawn on by the mystery of the earth’s fate, watching with a strange fascination the sun grow larger and duller in the westward sky, and the life of the old earth ebb away. At last, more than thirty million years hence, the huge red-hot dome of the sun had come to obscure nearly a tenth part of the darkling heavens.
The imagery was powerful in late Victorian England and it’s still powerful today. The dread of ‘that remote and awful twilight’ overcomes the time traveler, who makes his way back to his own time for a last encounter with his friends before disappearing forever. Maybe because of an early reading of Wells’ novel, I’ve always been fascinated with stars at the end of their lifetimes, stars that, like our Sun, will exhaust their hydrogen fuel and grow into red giants, engulfing their inner planets and possibly offering an opportunity for life on outer worlds and moons.
Image: I think that’s a Richard Powers cover on this old Berkley paperback (check out the handling of the time machine itself, surely a Powers signature). In any event, it gets across the beach scene in the novel, with the suggestion of a crab-like creature at right and, in the sky, a swollen, dying Sun.
Dying Stars, Migrating Planets
Enter HIP 13044 b, a newly discovered planet around a most interesting star. This is a gas giant with a minimum mass 1.25 times that of Jupiter, and it’s intriguing because it has survived the period of massive stellar expansion. HIP 13044, its host star, has contracted once again and is now burning helium in its core, a ‘horizontal branch star’ of the kind that planet hunters have generally had little to do with. But the European team using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile has its eye on dying stars and the planets that have survived their death throes, says Johny Setiawan (Max-Planck-Institut für Astronomie):
“This discovery is part of a study where we are systematically searching for exoplanets that orbit stars nearing the end of their lives. This discovery is particularly intriguing when we consider the distant future of our own planetary system, as the Sun is also expected to become a red giant in about five billion years.”
And just what happens to a planet in a situation like this? We have much to learn, but we do know that HIP 13044 b is, at its closest point in an elliptical orbit, less than a single stellar diameter from the surface of the star, about 0.055 AU, completing an orbit every 16.2 days. The researchers believe the planet’s orbit might once have been larger, but contracted during the red giant phase that would have swallowed the star’s inner planets, assuming they existed.
But at least some evidence points to their existence. HIP 13044’s fast rotation, higher than the norm for a horizontal branch star, can be explained by assuming that the star swallowed its inner planets during the red giant phase, which would have caused its spin to increase.
An Extragalactic Wanderer
The same fate probably awaits HIP 13044 b, for its host star will begin to expand once again in what could be a glimpse of the future for planets like our own Jupiter. But HIP 13044 b intrigues us on other grounds as well. Its primary contains few metals, elements above hydrogen and helium, causing Setiawan to add, “It is a puzzle for the widely accepted model of planet formation to explain how such a star, which contains hardly any heavy elements at all, could have formed a planet. Planets around stars like this must probably form in a different way.”
Moreover, the new planet orbits a star that is not native to the Milky Way at all, but a part of the Helmi stream, a collection of stars born in a dwarf galaxy and captured by the Milky Way between six and nine billion years ago. So we have a planet that is, despite its long tenure in our own galaxy, an extragalactic world, one found through radial velocity studies using the FEROS spectrograph. HIP 13044 b is about 2000 light years from Earth in the constellation Fornax.
We’ve had tentative detections of planets in other galaxies through gravitational microlensing, but no extragalactic planet has yet been confirmed, so HIP 13044 b is the next best thing, a galactic wanderer that found its way to the Milky Way before our own system had even formed. What for H.G. Wells was a scene of the remotest futurity may have played itself out in the unthinkably remote past for any beings that may have existed in the HIP 13044 system. In any case, it’s a system that has much to tell us about planetary fates around red giant stars.
The paper is Setiawan et al., “A Giant Planet Around a Metal-poor Star of Extragalactic Origin,” Science Express 18 November 2010 (abstract).
Comments on this entry are closed.
I always thought H.G.Wells showed particularly good sense in depicting the dying Sun as a red giant star. At the time Wells wrote the Time Machine (the 1890’s), Sir Norman Lockyer, the founder and editor of Nature, was pushing his theory of stellar evolution in which red giants are young, and dwarf stars, like the Sun, are old. Although this theory was not widely accepted by other astronomers (Hearnshaw, The Analysis of Starlight, 1986, page 93), it would have been easy for Wells to have been swayed by the opinions of such a prominent British figure.
Wells was depicting the dying Sun according to the Helmholtz contraction theory, meaning his timescale was all skew. Stephen Baxter cleverly ‘corrected’ Wells in his sequel to “The Time Machine”, “The Time Ships”, in which the Time Traveller discovers the truth about Morlocks (sort of.) Seems the bloated Red Sun was the result of stellar engineering gone horribly wrong.
Allan Sandage was certainly a giant in Astronomy for better then half a century. What a legacy he has left behind for Cosmology and Astronomy.
Dr. Brian Marsden passed away today at the age of 73 following a prolonged illness. He was a Supervisory Astronomer at the Smithsonian Astrophysical Observatory and Director Emeritus of the Minor Planet Center.
“Brian was one of the most influential comet investigators of the twentieth century,” said Charles Alcock, Director of the Harvard-Smithsonian Center for Astrophysics, “and definitely one of the most colorful!”
Dr. Marsden specialized in celestial mechanics and astrometry, collecting data on the positions of asteroids and comets and computing their orbits, often from minimal observational information. Such calculations are critical for tracking potentially Earth-threatening objects. The New York Times once
described Marsden as a “Cheery Herald of Fear.”
Full article here:
Brian Marsden has been running the Minor Panet Center for almost forever.
Who will be able to fill those shoes?
Marsden and Sandage will be missed. The passing of these respected pioneers makes me feel old.
Did the authors give any thought to the possibility that the composition of HIP 13044 b is the result of the planet pulling material from the star when it was larger?
Can planets circling red giant stars have life?
Wednesday, November 30, 2011
Allan Sandage…a new paper by Lynden-Bell and Schweizer
Allan Sandage was an observational astronomer who was happiest at a telescope. On Hubble’s sudden death Allan Sandage inherited the programmes using the world’s largest optical telescope at Palomar to determine the distances and number counts of galaxies.
Over many years he greatly revised the distance scale and, on re-working Hubble’s analysis, discovered the error that had led Hubble to doubt the interpretation of the galaxies’ redshifts as an expansion of the universe. Sandage showed that there was a consistent age of Creation for the stars, the elements and the Cosmos.
Through work with Baade and Schwarzschild he discovered the key to the interpretation of the colour–magnitude diagrams of star clusters in terms of stellar evolution.
With others he founded Galactic Archaeology, interpreting the motions and elemental abundances of the oldest stars in terms of a model for the Galaxy’s formation. He published several fine atlasses and catalogues of galaxies and a definitive history of the Mount Wilson Observatory.
“ALLAN R. SANDAGE” by Donald Lynden-Bell and Francois Schweizer
“Are our textbooks wrong? Astronomers clash over Hubble’s legacy”
“Edwin Hubble’s contributions to astronomy earned him the honor of
having his name bestowed upon arguably the most famous space telescope
(the Hubble Space Telescope, HST). Contributions that are often
attributed to him include the discovery of the extragalactic scale
(there exist countless other galaxies beyond the Milky Way), the
expanding Universe (the Hubble constant), and a galaxy classification
system (the Hubble Tuning Fork). However, certain astronomers are
questioning Hubble’s pre-eminence in those topics, and if all the
credit is warranted.”
10 April 2013
** Contacts are listed below. **
Text & Image:
DISCOVERY OF A BLUE SUPERGIANT STAR BORN IN THE WILD
A duo of astronomers, Dr. Youichi Ohyama (Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan) and Dr. Ananda Hota (UM-DAE Center for Excellence in the Basic Sciences, India), has discovered a blue supergiant star located far beyond our Milky Way Galaxy in the constellation Virgo.
Over 55 million years ago, it emerged in an extremely wild environment, surrounded by intensely hot plasma (a million degrees Celsius) and amidst raging cyclone winds blowing at 4 million kilometers per hour. Research using the Subaru Telescope, the Canada-France-Hawaii-Telescope (CFHT), and NASA’s ï¿œGalaxy Evolution Explorer (GALEX) revealed unprecedented views of the star formation process in this intergalactic context and showed the promise of future investigations of a possibly new mode of star formation, unlike that within our Milky Way.
About 1,000 galaxies reside in a cluster filled with million-degree hot plasma and dark matter. The Virgo cluster, the nearest cluster of galaxies located about 55 million light-years from Earth in the constellation Virgo, is an ideal laboratory to study the fate of gas stripped from the main body of galaxies falling into the intra-cluster medium. Does star formation take place in the clouds of stripped gas? If so, how? Dr. Ohyama and Dr. Hota focused on the trail of IC 3418 to explore a potentially new mode of star formation. Dr. Hota has been collecting data from multiple telescopes since 2006 to understand this galaxy, which he first spotted in the GALEX data during his Ph.D. research.
IC 3418 is a small galaxy falling into the Virgo cluster of galaxies at such a high speed (1,000 kilometers per second) that its blanket of cool gas strips off. As it passed through the cluster, its stripped-off cool gas formed a 55,500 light-years-long trail that looks very much like the water vapor condensation trail from a supersonic jet’s path. Hot plasma surrounds the trail of IC 3418, and it has not been clear whether the clouds of cool gas would vaporize like water sprinkled on a hot frying pan or condense further to form new young massive stars. The GALEX ultraviolet image shows that new massive stars do form in the trail. How did the stripped gas condense to form new stars without getting vaporized by the hot plasma? This process does not conform to star formation in our Milky Way Galaxy where massive stars develop in groups inside of stellar nurseries sheltered within giant, cold molecular gas clouds.
Dr. Ohyama suspected that a tiny dot of light emission in the trail of IC 3418 might be different from other blobs of ultraviolet light emissions in the trail. Spectroscopy of the little dot from Subaru Telescope’s Faint Object Camera and Spectrograph (FOCAS) revealed something stunning. Dr. Ohyama recalls, “When I first saw the spectrum, I was so puzzled, since it did not look like anything I had known of in extragalactic astronomy.” Unlike typical star-forming regions, the telltale signs of stellar nurseries were missing.
Intense UV-radiation usually ionizes/heats-up the surrounding gas when a star is born. Instead of any sign of heated gas, the observation showed fast winds blowing out of the stellar atmosphere at a speed of about 160 kilometers per second. Comparison with emissions from nearby stars made it clear that this massive, hot (O-type) star had passed its youth and was now aging; it was at a stage known as a blue supergiant star and would soon face its explosive death as a supernova.
Dr. Ohyama commented on the significance of the research: “If our interpretations are correct, this is probably the farthest star ever discovered with spectroscopic observation. Since we only observed for a fraction of the night with the 8.2-meter Subaru Telescope, there is huge potential for stellar spectroscopy with extremely large telescopes, e.g., the Thirty Meter Telescope, being planned for the future. We look forward to that exciting time.”
Dr. Hota emphasized how important it is for astronomers to pay attention to this exotic system: “Precisely because the thermal and dynamic contrast of star formation that our research shows cannot be observed within our Milky Way, the details revealed by the Subaru Telescope’s spectroscopy and the deep, sharp imaging of CFHT are opening up a new avenue for investigating the baffling fundamentals of star formation.” Future in-depth investigations of this cocktail of hot plasma and turbulent, cold gas may reveal very different characteristics of stars, which may remain wild, exotic objects, challenging current theories of star formation.
Suzanne G. Frayser
Subaru Telescope, Hawaii
Dr. Ananda Hota
UM-DAE Center for Excellence in Basic Sciences
Vidyanagari, Mumbai, India
+91 86 007 125 08
The research paper entitled “Discovery of a Possibly Single Blue Supergiant Star in the Intra-Cluster Region of Virgo Cluster of Galaxies” on which this article is based was published in the Astrophysical Journal Letters, Volume 767, No. 2. http://iopscience.iop.org/2041-8205/767/2/L29
Three other galaxies similar to IC 3418 were studied earlier by the Hubble Space Telescope, Subaru Telescope, and GALEX. Refer to the following links for more information:
* HST: “Hubble Sees ‘Comet Galaxy’ Being Ripped Apart by Galaxy Cluster” http://hubblesite.org/newscenter/archive/releases/2007/12/image/a/
* Subaru: “Galaxy Ramming Through Space Creates Fireballs” http://subarutelescope.org/Pressrelease/2008/10/06/index.html
* GALEX: “Astronomers Discover Star-Studded Galaxy Trail” http://www.galex.caltech.edu/newsroom/glx2010- 02f.html
Pseudo-color GALEX ultraviolet image of the galaxy IC 3418 falling into the Virgo cluster. Notice the young star-forming clumps in its 55,000 light-years-long trail, as the galaxy moves towards the top-right area. Zooming into one of the blobs, marked by the arrow, the color optical image from CFHT shows the bright Blue Supergiant star in the middle of the inset image on the top-left area. The optical spectrum from the same star (bottom-right area), which was obtained by Subaru Telescope’s Faint Object Camera and Spectrograph (FOCAS), shows only one bright red emission line (H-alpha) due to the stellar wind and none of the other usual signs of star-forming regions. (Credit: NAOJ, CFHT, GALEX, Y. Ohyama & A. Hota)
This research was partially supported by the following:
* National Science Council of Taiwan (grant to Dr. Ohyama)
* National Center for Radio Astrophysics of Tata Institute of Fundamental Research (NCRA-TIFR) and Inter-University Center for Astronomy and Astrophysics (IUCAA), and, both in India (for Visiting Astronomer position to Dr. Hota).