Astronomy Archives

March 22, 2009December 24, 2015 by Anne Minard

Star Exploded Too Early, May Blow Apart Supernova Theory

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NASA’s Hubble Space Telescope has identified a star a million times brighter than the sun that exploded as a supernova in 2005 — well before it should have, according to current theories of stellar evolution.

The doomed star, estimated at about 100 times our sun’s mass, was not mature enough, according to theory, to have evolved a massive iron core of nuclear fusion ash. This is the supposed prerequisite for a core implosion that triggers a supernova blast.

“This might mean that we are fundamentally wrong about the evolution of massive stars, and that theories need revising,” says Avishay Gal-Yam of the Weizmann Institute of Science, in Rehovot, Israel. The finding appears in the online version of Nature Magazine.

The explosion, called supernova SN 2005gl, was seen in the barred-spiral galaxy NGC 266 on October 5, 2005. NGC 266 is about 200 million light years away, in the constellation Pisces.

The progenitor was so bright that it probably belonged to a class of stars called Luminous Blue Variables (LBVs), “because no other type of star is as intrinsically brilliant,” says Gal-Yam. But there’s a wrinkle: as an LBV-class star evolves, it sheds much of its mass through a violent stellar wind. Only at that point does it develop a large iron core and ultimately explodes as a core-collapse supernova.

“The progenitor identification shows that, at least in some cases, massive stars explode before losing most of their hydrogen envelope, suggesting that the evolution of the core and the evolution of the envelope are less coupled than previously thought, a finding which may require a revision of stellar evolution theory,” co-author Douglas Leonard, from California’s San Diego State University, said in a press release.

One possibility is that the progenitor to SN 2005gl was really a pair of stars — a binary system — that merged. This would have stoked nuclear reactions to brighten the star enormously, making it look more luminous and less evolved than it really was.

“This also leaves open the question that there may be other mechanisms for triggering supernova explosions,” says Gal-Yam. “We may be missing something very basic in understanding how a superluminous star goes through mass loss.”

Gal-Yam and Leonard located the progenitor in archival images of NGC 266 taken in 1997. They then used the Keck telescope to precisely locate the supernova on the outer arm of the galaxy. A follow-up observation with Hubble in 2007 unequivocally showed that the superluminous star was gone.

Extremely massive and luminous stars topping 100 solar masses, such as Eta Carinae in our own Milky Way Galaxy, are expected to lose their entire hydrogen envelopes prior to their ultimate explosions as supernovae.

“These observations demonstrate that many details in the evolution and fate of LBVs remain a mystery,” said Mario Livio, of the Space Telescope Science Institute in Baltimore. “We should continue to keep an eye on Eta Carinae – it may surprise us yet again.”

MOSAIC CAPTIONS: [Top Center] 2005 ground-based image of the supernova; [Bottom Left] 1997 Hubble archival visible-light image of the region of the galaxy where the supernova exploded, with white circle marking the progenitor star; [Bottom Center] Near-infrared light photo of the supernova explosion taken on Nov. 11, 2005, with the Keck telescope, with the blast centered on the position of the progenitor; [Bottom Right] Visible-light Hubble follow-up image taken on September 26, 2007. The progenitor star is gone. Credit: NASA, ESA, and A. Gal-Yam (Weizmann Institute of Science, Israel)

Source: HubbleSite

March 20, 2009December 24, 2015 by Tammy Plotner

SkyWatcher’s Forecast: March 20-26, 2009 – A Messier Marathon Special Edition!

Greetings, fellow SkyWatchers! That’s right… It’s that time again. Equinox and upcoming New Moon means that many of us are going to try and kill ourselves to capture all 110 Messier Catalog objects in just one night. When I was a much younger lass, I used to think that was fun. Now that I’m considerably older and have to pay a physical price for staying outside all night in the cold? Well… It’s not quite as appealing as it used to be. But, I ain’t ready for the dirt nap just yet. If you think you’ve still got what it takes, then follow me…

Friday, March 20, 2009 – Since the beginning of the year, the Sun has been traveling low in the sky, moving higher each day until reaching northern hemisphere vernal equinox. Today the Sun will rise exactly in the east and set exactly in the west – precisely 12 hours later – making it possible for most observers to see all 110 Messier objects in a single night. The Messier Marathon isn’t easy. This year,why not try your own style of marathoning, as we take a less frenzied pace over the next 11 days, enjoying these splendid objects ‘‘ten at a time.’’

When the sky darkens enough to find guidestar Delta Ceti, the M77 (RA 02 42 40.83 Dec -00 00 48.4) spiral galaxy will be your first and the M74 (RA 01 36 41.84 Dec +15 46 59.6) spiral galaxy east of Eta Pisces will be your second mark. Both are telescopic only, and an extreme challenge due to low position. Next is M33, west of Alpha Triangulum. With ideal skies, the Pinwheel Galaxy can be seen in binoculars, but sky glow makes this huge, low-surface brightness spiral difficult for even telescopes at low power. M31 (RA 00 42 44.31 Dec +41 16 09.4), the Andromeda Galaxy, is a delightful capture for both binoculars and scopes just west of Nu Andromedae. For the telescope, two more on the list are companions to M31: elliptical M32 (RA 00 42 41.87 Dec +40 51 57.2) on its southeastern edge, and M110 (RA 00 40 22.00 Dec +41 41 07.0), to the northwest.

Head northwest for two open clusters visible to both telescopes and binoculars. You’ll find M52 (RA 23 24 48.00 Dec +61 35 -0.0) easiest by identifying Alpha and Beta Cassiopeiae, drawing a mental line between them, and extending it the same distance northwest of Beta. Next, hop north of Delta Cassiopeiae to pick up our eighth object—open cluster M103 (RA 01 33 24.00 Dec +60 39 00.0). Head south toward Perseus to telescopically locate the M76 (RA 01 42 19.95 Dec +51 34 31.1) planetary nebula just north of Phi. Binoculars are all that’s needed to see M34, an open cluster located roughly halfway between Algol and the lovely double Almach. As you can see, such a quick journey takes away some of the beauty of learning the history and science behind the objects… But the race is on!

Saturday, March 21, 2009 – Today, note the 1927 birth on this date of Halton Christian Arp, one of the most noted minds of our time regarding the origin and evolution of galaxies. Through his incredible study of peculiar galaxies and quasars, we are no longer able to assume that redshift is a uniform indicator of distance, or that the two are unrelated.

Tonight our marathon will be more relaxed because the fastest-setting objects are already completed. Take a moment to enjoy M45 (RA 03 47 24.00 Dec +24 07 00.0), the Pleiades. The ‘‘Seven Sisters’’ are easily visible high in the west, and their cool, blue beauty is incomparable in binoculars or telescopes. Head for Lepus and identify Beta and Epsilon. Triangulating south with this pair is 5th-magnitude star ADS3954, and the small globular M79 (RA 05 24 10.59 Dec -24 31 27.3) to its northeast. M42 (RA 05 35 17.30 Dec -05 23 28.0) , the Orion Nebula, is next. M43 (RA 05 35 31.00 Dec -05 16 12.0) is part of M42 to the north northeast. The next two objects are M78 (RA 05 46 46.70 Dec +00 00 50.0), northeast of Zeta Orionis and M1 (RA 05 34 31.97 Dec +22 00 52.1), the Crab Nebula, northwest of Zeta Tauri.

Now take a few minutes to relax. The remaining objects on tonight’s list are all very easy, well positioned, and observable with binoculars. Are you ready? Then let’s go! Open cluster M35 (RA 06 09 06.00 Dec +24 21 00.0) is northwest of the toe of Gemini – Eta. The next stop is Auriga, directly between Theta and southern Beta. Slightly to the east you’ll find open cluster M37 (RA 05 52 19.00 Dec +32 33 12.0). Now use Theta and western Iota. Roughly halfway between them and in the center of Auriga you will find open cluster M38 (RA 05 28 43.00 Dec +35 51 18.0). Hop southeast to capture M36 (RA 05 36 12.00 Dec +34 08 24.0).

Although this pace may seem rather scandalous, take stock of what you’ve accomplished! You’ve visited 20 Messier objects in just two nights. . .with time to spare. Return to your favorite objects and enjoy them. As Halton Arp once said:

“Sometimes I think that Astronomy is not so much a science as a series of scandals.”

Sunday, March 22, 2009 – Born on this date in 1394 was Ulugh Beg, builder of the first observatory. Beg’s chart listed 994 stars and was the first produced since Hipparchus! In 1799, Friedrich Wilhelm August Argelander, who cataloged the positions and magnitudes of 324,188 variable stars, was born!

Now get Sirius, go south, and start our list for tonight with open cluster M41. Return to Sirius and head a fist-width east/northeast for M47 (RA 07 36 36.00 Dec -14 29 -0.0). Dimmer, more compressed M46 (RA 07 41 42.00 Dec -14 49 00.0) is east. Drop slowly south about three fingerwidths and encounter lively M93 (RA 07 44 36.00 Dec -23 52 00.0)! Incredibly colorful open cluster M50 (RA 07 02 40.47 Dec -08 21 50.5) is roughly one-third the distance between Sirius and Procyon. Drop south-southeast of Zeta Monocerotis for dim open cluster M48 (RA 08 13 42.00 Dec -05 45 00.0). The ‘‘Beehive’’ – M44 (RA 08 40 24.00 Dec +19 41 -0.0) – is just north-northwest of Delta Cancri. Continue south to Alpha, and then west for M67 (RA 08 51 18.00 Dec +11 48 00.0). It will appear as a fine haze to binoculars, but telescopes see a spectacular cloud of similar magnitude resolvable stars.

Telescopes, head a fist-width east Regulus for finderscope stars 52 and 53, and head between them. Just about 1.5 degrees south of 52 is elliptical galaxy M105 (RA 10 47 49.60 Dec +12 34 53.9). Larger scopes see two additional faint galaxies, NGC 3384 and NGC 3389, to M105’s west. Continue another degree south toward star 53 for the silver-gray beauty of M96 (RA 10 46 45.78 Dec +11 49 10.2). Enjoy its bright nucleus and wispy arms!

Now relax and enjoy a spring evening with two meteor showers. The northern hemisphere Camelopardalids have no definite peak, and a fall rate of only 1 per hour. They’re the slowest recorded meteors, entering our atmosphere at speeds of only 7 kilometers per second! Far more interesting for both hemispheres is tonight’s peak of the March Geminids. These slower than normal meteors will be fun to watch! When you see a bright streak, trace it back to its point of origin: which did you see, a Camelopardalid, or a March Geminid?

Monday, March 23, 2009 – In 2001 on this date the Mir space station ended 15 years in orbit with a fiery return. This date is also the 1837 birth of Richard Anthony Proctor who showed the stars’ motion, distribution, and relation to nebulae. In 1829, Norman Pogson, creator of the magnitude scale still used today, was born. The year 1749 saw the birth of Pierre-Simon Laplace, who theorized that the Solar System formed from a nebula, formulated mathematical probability, and helped create the metric system!

Return to Leo tonight. Identify 52 Leonis and drop south past M105 for M95 (RA 10 43 57.70 Dec +11 42 13.7), which isn’t as bright or large as neighboring M96 (RA 10 46 45.78 Dec +11 49 10.2). Small scopes see central brightening, and large ones begin resolution of this awesome barred spiral. Look to the southwestern star of the three marking Leo’s hips – Theta Leonis. South is faint star 73, and a degree east-southeast is the pairing of M65 and M66. Western M65 (RA 11 18 55.78 Dec +13 05 32.3) and eastern M66 (RA 11 20 15.07 Dec +12 59 21.6) are both beautiful spirals worthy of far more time and attention. Head north for another same-field pair – M81 and M82 – in Ursa Major. Draw a mental line between Gamma and Alpha. Extend the line beyond Alpha the same distance. Begin an eyepiece sweep to locate them. The southernmost is stunning, bright-cored M81 (RA 09 55 33.17 Dec +69 03 55.1). North is the broken, spindle-shaped peculiar galaxy M82 (RA 09 55 52.19 Dec +69 40 48.8). Southeast of Beta Ursae Majoris (UM) is the edge-on galaxy M108 (RA 11 11 31.29 Dec +55 40 31.0).

Continue another half degree southeast for the Jupiter-sized planetary M97 (RA 11 14 47.73 Dec +55 01 08.5). Continue south to Gamma UM for same-field M109 (RA 11 57 35.90 Dec +53 22 35.0). The last in Ursa Major is an error on Messier’s part. M40 (RA 12 22 24.00 Dec +58 05 -0.0) is actually double star WNC4, located northeast of 70 Ursae Majoris. Now to Canes Venatici and our last object tonight: Alpha and northern Beta are easily recognizable to the east of the last star in the handle of the Big Dipper (Eta). You’ll find the soft-spoken spiral galaxy M106 (RA 12 18 57.54 Dec +47 18 14.3) almost directly midway between Beta CVn and Gamma UM less than 2 degrees south of star 3. Add as much aperture as you can to this gorgeous study!

Tuesday, March 24, 2009 – On this date in 1835 Josef Stefan was born, a physicist whose word was ‘‘law’’ to radiation! In 1941 on this date, Joseph Taylor, Jr, the radio astronomer who jointly discovered the first binary pulsar, was born. Last, let’s celebrate the 1893 birth of Walter Baade, who studied the Andromeda Galaxy’s core with the 100’’ Hooker telescope, resolving it (and two different Cepheids) for the first time.

Tonight, identify Canes Venatici’s two brightest stars, Alpha and Beta. Galaxy M94 (RA 12 50 52.63 Dec +41 07 09.3) forms a triangle with Alpha and Beta CnV, the apex toward Eta Ursae Majoris (UM). M63 (RA 13 15 49.28 Dec +42 01 46.5) is one-third the distance between Beta CnV and Eta UM. M51 (RA 13 29 52.37 Dec +47 11 40.8) resides near visual star 24 CnV. You’ll find M101 (RA 14 03 12.51 Dec +54 20 53.1) to the other side of Alkaid. The accepted designation for M102 (RA 14 03 12.59 Dec +54 20 56.7) is lenticular galaxy NGC 5866, located southeast of Iota Draconis. You’ll find small globular cluster M53 (RA 13 12 55.30 Dec +18 10 09.0) northeast of Alpha Comae. M64 (RA 12 56 43.88 Dec +21 41 00.1) is about one-third the distance from Alpha Comae to Eta UM. M3 (RA 13 42 11.23 Dec +28 22 31.6) is one-third the distance between Arcturus and Cor Caroli.

Now for the incredibly rich galaxy fields near Coma Berenices and Virgo. Identify the easternmost star in Leo – Denebola – and head a fist-width due east. M98 (RA 12 13 48.29 Dec +14 54 01.2) is west of star 6 Comae. Return to 6 Comae and drop 1 degree southeast for M99 (RA 12 18 49.52 Dec +14 25 00.4).

Congratulations! In just 5 days you have logged 50 of the brightest and most beautiful members of the deep sky!

Wednesday, March 25, 2009 – Today celebrates the 1786 birth of Giovanni Amici, inventor of the achromatic lens, and in 1923, the birth of Kenneth Linn Franklin, radio astronomer. Tonight continue our marathon around midnight. It’s time to dance…

Leo’s easternmost bright star Denebola points to 6 Comae, about three finger-widths east. Two degrees northeast of 6 you’ll pass two 5th-magnitude stars leading to M100 (RA 12 22 54.95 Dec +15 49 19.5), the largest-appearing galaxy in the Coma-Virgo cluster. Continue 2 degrees north for bright yellow 11 Comae. One degree northeast is 9th magnitude, round M85 (RA 12 25 24.23 Dec +18 11 26.9). Try a “trick of the trade” to locate two more. Return to 6 Comae, relocate M99, turn off your drive, and take a break for 14 minutes. When you return, the elongated form and near-stellar nucleus of M88 (RA 12 31 59.34 Dec +14 25 13.4) will have ‘‘drifted’’ into view. Wait another 2–3 minutes, and the faint, barred spiral M91 (RA 12 35 26.58 Dec +14 29 45.1) will join the show in a 1-degree field of view.

Now locate bright Vindemiatrix (Epsilon Virginis), a handspan due east of Denebola. Hop 4.5 degrees west and a shade north to locate the largest elliptical galaxy presently known, M60 (RA 12 43 40.19 Dec +11 33 08.9). This magnitude 9 galaxy can be spotted with binoculars, but a telescope will reveal faint NGC4647, which only appears to be interacting with M60. In the field west is our next Messier: bright-cored elliptical M59 (RA 12 42 02.39 Dec +11 38 45.1). (Yes, there’s more, but not tonight. Let’s keep our studies to only the Messiers!) Move a degree west for fainter M58 (RA 12 37 43.48 Dec +11 49 04.4). About a degree north will locate face-on spiral M89 (RA 12 35 39.81 Dec +12 33 22.8). One half degree northeast is delightful 9.5 magnitude M90 (RA 12 36 50.08 Dec +13 09 45.7), whose dark dust lanes show in larger scopes. Continue 1.5 degrees southwest for M87 (RA 12 30 49.42 Dec +12 23 28.0), the first radio source galaxy discovered. M87 contains a black hole, and more than 4,000 globular clusters surround its elliptical form.

Now take a break… Things are about to get a lot hotter!

Thursday, March 26, 2009 – Starting at midnight now. Dawn is only a few hours away and the beginning of a new day. It is also a New Moon and the perfect time to try all 110 Messier objects in just one night! What’s that? You want to keep on going ten at a time? Then let’s do just that…

Slightly more than a degree northwest of M87 is the same-field pair, western M84 (RA 12 25 03.74 Dec +12 53 13.1) and eastern M86 (RA 12 26 12.20 Dec +12 56 44.5). Head to 31 Virginis and identify splendid variable R a degree west. Two degrees northwest is galaxy M49 (RA 12 29 46.76 Dec +07 59 59.9). Shift 3 degrees southwest for the handsome yellow double 17 Virginis. A half degree south is large face-on spiral M61. Now go for Spica, and 11 degrees due west. M104 (RA 12 39 59.43 Dec -11 37 23.0), the Sombrero Galaxy, will be your reward for a job well done. Congratulations! You’ve just seen 15 of the finest galaxies in the Coma–Virgo region in just hours, and our “Marathon” continues.

Five degrees south-southeast of Beta Corvi is your marker star, the double A8612, for the same field globular M68 (RA 12 39 28.01 Dec -26 44 34.9), and the Southern Pinwheel, M83 (RA 13 37 00.78 Dec -29 51 58.6) is 10 degrees southeast of Gamma Hydrae. Now make a wide move and head southeast of Arcturus for Alpha Serpentis. Eight degrees southwest is outstanding globular cluster M5 (RA 15 18 33.75 Dec +02 04 57.7) sharing the field with 5 Serpens. Now locate the ‘‘keystone’’ shape of Hercules, and identify Eta in its northwest corner. One-third the way between it and southern Zeta is the fantastic M13 (RA 16 41 41.44 Dec +36 27 36.9), the “Great Hercules Globular Cluster.” More difficult is M92 (RA 17 17 07.27 Dec +43 08 11.5), because there are no stars to guide you. Try this trick: using the two northernmost stars in the “keystone” asterism and form an equilateral triangle in your mind, with its apex to the north. Point your scope there. Way to go, astronomer! You have now passed the most difficult part of the “mini-thon,” and just think of the rewards! In less than a week, you have conquered over half of the Messier catalog.

While you spend a sleepy day, think about a French amateur astronomer who was watching a round black spot transit the Sun today in 1859. His name was Lescarbault, and he was sure he’d witnessed a new planet, which he christened “Vulcan.” Nathaniel Bowditch was also born this date in 1773. He also devised the “Bowditch Curve,” which applies in both physics and astronomy.

Be sure to join us next Friday as we conclude our Messier Marathon special! Until then? Dreams really do come true when you keep on reaching for the stars….

This week’s awesome images are (in order): M74 and M34 (credit – Palomar Observatory, courtesy of Caltech), Halton Arp (historical image), M38, M96, M106, M99, M87 and M61 (credit – Palomar Observatory, courtesy of Caltech). Thank you so much!!

March 19, 2009December 24, 2015 by Nancy Atkinson

Astronomers Observe Bizarre Blazar with Battery of Telescopes

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Quasars visible at gamma-ray energies are called “blazars.” Blazars are among the most energetic objects in the universe and are fueled by supermassive black holes at the core of certain giant elliptical galaxies. An international team of astrophysicists using a combination of ground- and space-based telescopes have uncovered surprising changes in radiation emitted by an active galaxy. The picture that emerges from these first-ever simultaneous observations with optical, X-ray and new-generation gamma-ray telescopes is much more complex than scientists expected and challenges current theories of how blazars generate the radiation they emit.

The galaxy, called PKS 2155-304, emits oppositely directed jets of particles traveling near the speed of light as matter falls into a central supermassive black hole; this process is not well understood. In the case of blazars, the galaxy is oriented such that we’re looking right down the jet.

PKS 2155-304 is located 1.5 billion light-years away in the southern constellation of Piscis Austrinus and is usually a detectable but faint gamma-ray source. But when its jet undergoes a major outburst, as it did in 2006, the galaxy can become the brightest source in the sky at the highest gamma-ray energies scientists can detect — up to 50 trillion times the energy of visible light. Even from strong sources, only about one gamma ray this energetic strikes a square yard at the top of Earth’s atmosphere each month.

Atmospheric absorption of one of these gamma rays creates a short-lived shower of subatomic particles. As these fast-moving particles rush through the atmosphere, they produce a faint flash of blue light. The High Energy Stereoscopic System (H.E.S.S), an array of telescopes located in Namibia, captured these flashes from PKS 2155-304.

One of the H.E.S.S. telescopes in Namabia. Credit: H.E.S.S.

Gamma rays at lower energies were detected directly by the Large Area Telescope (LAT) aboard NASA’s orbiting Fermi Gamma-ray Space Telescope. “The launch of Fermi gives us the opportunity to measure this powerful galaxy across as many wavelengths as possible for the first time,” says Werner Hofmann, spokesperson for the H.E.S.S. team at the Max-Planck Institute for Nuclear Physics in Heidelberg, Germany.

With the gamma-ray regime fully covered, the team turned to NASA’s Swift and Rossi X-ray Timing Explorer (RXTE) satellites to provide data on the galaxy’s X-ray emissions. Rounding out the wavelength coverage was the H.E.S.S. Automatic Telescope for Optical Monitoring, which recorded the galaxy’s activity in visible light.

Between August 25 and September 6, 2008, the telescopes monitored PKS 2155-304 in its quiet, non-flaring state. The results of the 12-day campaign are surprising. During flaring episodes of this and other blazars, the X- and gamma-ray emission rise and fall together. But it doesn’t happen this way when PKS 2155-304 is in its quiet state — and no one knows why.

What’s even stranger is that the galaxy’s visible light rises and falls with its gamma-ray emission. “It’s like watching a blowtorch where the highest temperatures and the lowest temperatures change in step, but the middle temperatures do not,” says Berrie Giebels, an astrophysicist at France’s École Polytechnique who works with both the H.E.S.S. and Fermi LAT teams.

“Astronomers are learning that the various constituents of the jets in blazars interact in fairly complicated ways to produce the radiation that we observe,” says Fermi team member Jim Chiang at Stanford University, Calif. “These observations may contain the first clues to help us untangle what’s really going on deep in the heart of a blazar.”

Source: NASA

March 19, 2009December 24, 2015 by Anne Minard

Disappearing Stars Confirm Supernova Origins

Artist's rendering of SN 1993J, where a red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). Credit: ESA

Artist’s rendering of SN 1993J, where a red supergiant supernova progenitor star (left) is exploding after having transferred about seven solar masses of hydrogen gas to the blue companion star (right). Credit: ESA

Astronomers have caught two stars in the disappearing acts that link them to type II supernova events.

Type II supernovae are widely believed to result from the internal collapse and explosion of massive stars, about nine times the size of our sun. But precious few observations have actually confirmed the relationship.

Now, researchers have spotted two parent stars that showed up in supernovae “before” images — but not in images taken after the blasts.

“The disappearance of the progenitors confirms that these two supernovae were produced by Red Supergiants,” write co-authors Justyn Maund and Stephen Smartt. Their new paper is out in this week’s issue of Science.

SN 2003gd. Credit: Gemini Observatory

So far only one star has been shown to have disappeared after it exploded — the star that exploded as SN 1987A in the Local Group of galaxies. Seven other stars have been spotted in the neighborhoods of type II supernovae before they went off, but none of them has been shown to have disappeared, Maund and Smartt write.

Maund is affiliated with both the University of Copenhagen in Denmark and the University of California at Santa Cruz, and Smartt is from Queen’s University Belfast in the UK. They used the Hubble Space Telescope and the Gemini Telescope to observe the two supernovae.

The progenitor of SN 2003gd, an M-supergiant star in the galaxy M74, “is no longer observed at the SN location,” they found. They estimated 2003gd is seven times the mass of the sun, which they acknowledge “is at the lower end of the mass range considered theoretically possible to produce core-collapse events.” They said there’s enough uncertainty in the object’s mass that it could be greater than seven solar masses — but even if it’s not, several other stars in the low end of the range are suspected of exploding as supernovae.

The co-authors are also careful to point out that dust from the supernova is still visible, and, “One could argue that the star identified as the progenitor was a neighboring star that is now obscured by dust formation.” But their work indicates that the explosion wasn’t dusty enough to obscure a star as luminous as SN 2003gd’s parent. They believe the progenitor star has truly disappeared — although further confirmation will come as the dust continues to clear.

SN 1993J is a truly exceptional case. The K-supergiant star that exploded in that supernova is also no longer present, the authors report — but its B-supergiant binary companion is still observed.

The model for the binary system was of a progenitor star 15 times the mass of the sun, with a slightly less massive binary companion. The progenitor star evolved faster, and transferred some of its mass onto the binary companion, including a substantial amount of its hydrogen envelope. The binary companion grew to 22 times the mass of the sun. The interaction happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J became known as one of the most peculiar supernovae ever seen.

The site of SN 1993J was imaged several times over the 2 to 13 years after the explosion with Hubble and a handful of other telescopes. By the 2004 observation, the red portion of the SN spectral energy distribution had faded below the level of the red spectral energy of the binary progenitor system, “ruling out the continued presence of the K-supergiant star and, hence, confirming it as the progenitor of SN 1993J,” the authors wrote.

They said soon the blue part of the supernova’s spectrum will fade, opening up a window for observations of the remaining companion star.

The authors conclude that their “simple, but time-consuming” method “leaves no doubt that the two stars were the progenitors of the supernovas, SN 2003gd and SN 1993J, and confirms that type II supernovas are birthed from Red Supergiants, as predicted.”

March 19, 2009January 24, 2021 by Tammy Plotner

Vernal Equinox – Busting the Myth of Balancing Eggs

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Spring officially arrives for everyone, including astronomers on March 20. The word “Equinox” literally means “equal night”. It’s all about the balance of light – not the myth of balancing eggs. On the universal date (UTC) of Friday, March 20, 2009 at 11:44 (am) both the day and night are the same length. But what’s so special about it? It’s a date that most of us recognize as symbolic of changing seasons. North of Earth’s equator we welcome Spring, while people south of the equator are gearing up for the cooler temperatures of Autumn. But what’s all this about balancing eggs?

These all too brief, but monumental moments in Earth-time, owe their significance to the slightly more than 23 degree tilt of the Earth’s axis. Because of our planetary angle, we in the northern hemisphere receive the Sun’s rays most directly during the Summer. In the Winter, when we are tilted away from the Sun, the rays pass through the atmosphere at a greater slant, bringing lower temperatures. If the Earth rotated on an axis perpendicular to the plane of the Earth’s orbit around the Sun, there would be no variation in day lengths or temperatures throughout the year, and we would not have seasons. At Equinox, the midway between these two times in Spring and Autumn, the spin axis of the Earth points 90 degrees away from the Sun.

If your head is spinning from all of this, sit and ponder for a moment. Now is a great time to choose a marker and observe what’s happening for yourself. Trying a real science experiment for equinox is much better than the myth of balancing eggs. Just place a stake of some type into the ground (or use a fencepost or signpost) and periodically over the next few weeks measure the length of the shadow when the Sun is at its highest and write down your measurements. I use my south facing deck railing and mark its shadow on the deck boards in chalk. It won’t take long before your marker’s shadow length changes and you notice how the Sun’s position changes in the sky, and with it the ecliptic plane.

In the language of astronomy, an equinox is either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The Vernal Equinox is also known as “the first point of Aries” – a the point at which the Sun appears to cross the celestial equator from south to north. This is also the the zero point of longitude – the reference plane at which right ascension is defined as 0. Believe it or not, this was defined in 1950 as the northern vernal equinox, but it has moved to the constellation of Pisces now! Why? The equinoxes are not fixed points on the celestial sphere but move westward along the ecliptic, passing through all the constellations of the zodiac in 26,000 years. This is what’s known as the precession of the equinoxes – a motion first noted by Hipparchus roughly in 120 B.C. But what causes it?

The precession is caused the gravitational attraction of both the Moon and Sun on the equatorial bulge of the Earth. Imagine the Earth’s axis patterning itself in a cone as it moves, like a spinning top. As a result, the celestial equator, which lies in the plane of the Earth’s equator, moves on the celestial sphere, while the ecliptic, which lies in the plane of the Earth’s orbit around the Sun, is not affected by this motion. The equinoxes, which lie at the intersections of the celestial equator and the ecliptic, now move on the celestial sphere. Much the same, the celestial poles move in circles on the celestial sphere, so that there is a continual change in the star at or near one of these poles.

After a period of about 26,000 years the equinoxes and poles lie once again at nearly the same points on the celestial sphere. Because the gravitational effects of the Sun and Moon aren’t always the same, there is some wobble in the motion of the Earth’s axis called nutation. This wobble causes the celestial poles to move, not in perfect circles, but in a series of S-shaped curves with a period of 18.6 years that was first explained by Isaac Newton in 1687.

So where did the urban myth of balance eggs on vernal equinox come from? Probably because at one time Easter was celebrated at this time and eggs play a very big role in the whole Esotere, rebirth, and cultural symbolism of this holiday. It may very well have been the good folks in China who orginally began the myth by patiently practicing standing eggs on end during vernal equinox to symbolize the restoration of balance to the world after a season of darkness. If this symbol of fertility could be balanced on such a day of significance, then surely nature was in harmony!

Go ahead and balance eggs for fun… But believe in science.

P.S. The Bad Astronomer Phil Plait has a tutorial video on his website, teaching you how to stand an egg on end, any time of the year. Click here to watch it.

Many thanks to Vasilij Rumyantsev (Crimean Astrophysical Obsevatory) for the excellent solar analemma as it appeared in the July 9, 2002 APOD.

March 19, 2009December 24, 2015 by Ian O'Neill

The Sun as a White Dwarf Star

Dusty debris around an old white dwarf star (NASA)

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What will happen to all the inner planets, dwarf planets, gas giants and asteroids in the Solar System when the Sun turns into a white dwarf? This question is currently being pondered by a NASA researcher who is building a model of how our Solar System might evolve as our Sun loses mass, violently turning into an electron-degenerate star. It turns out that Dr. John Debes work has some very interesting implications. As we use more precise techniques to observe existing white dwarf stars with the dusty remains of the rocky bodies that used to orbit them, the results of Debes’ model could be used as a comparison to see if any existing white dwarf stars resemble how our Sun might look in 4-5 billion years time…

A comparison of the Sun in its yellow dwarf phase and red giant phase

Today, our Sun is a healthy yellow dwarf star. If you want to be precise, it is a “G V star”. This yellow dwarf will happily burn 600 million tonnes of hydrogen per second in its core for 10 billion years, generating the light that is required to make our planet habitable. The Sun is approximately half-way through this hydrogen burning phase, so it’s OK, things aren’t going to change (for the Sun at least) for a long time yet.

But what happens then? What happens in 4-5 billion years when the supply of hydrogen runs out in the core? Although our Sun isn’t massive enough to entertain the thought of going out in a blaze of supernova glory, it will still go through an exciting, yet terrifying death. After evolving through the hydrogen-burning phase, the Sun will puff up into a huge red giant star as the hydrogen fuel becomes scarce, expanding 200 times the size it is now, probably swallowing the Earth. Helium, and then progressively heavier elements will be fused in and around the core. The Sun will never fuse carbon however, instead it will shed its outer layers forming a planetary nebula.

Once things calm down, a small sparkling jewel of a white dwarf star will remain. This tiny remnant will have a mass of around half that of our present Sun, but will be the size of the Earth. Needless to say, white dwarfs are very dense, intense gravitational pull countered not by fusion in the core (like all Main Sequence stars), but by electron degeneracy pressure.

Relative sizes of IK Pegasi A (left), IK Pegasi B (lower center; a white dwarf) and the Sun (NASA)

When the Solar System reaches this phase in its evolution, what will it look like? What will become of the asteroids, gas giants, moons and rocky planets? I was very fortunate to chat with astrophysicist Dr John Debes, from NASA’s Goddard Space Flight Center, at January’s American Astronomical Society (AAS) conference in Long Beach (California) who is developing an n-body code simulating an evolving Solar System.

After the Sun has stopped hydrogen fusion in its core, it loses mass as it sheds its outer layers after the red giant phase and subsequent planetary nebula formation. It is estimated that the Sun will lose about 50% of its mass during this time, naturally affecting the Solar System as a whole. As the Sun loses mass, the outer planets (such as Jupiter) will drift outwards, increasing their orbital radii. In the simulation, Debes is very careful to ensure there is a gradual reduction in solar mass to ensure stability in the simulation.

What we are left with is an old Solar System, where little is left of the inner planets (it is likely that anything within the orbit of the Earth will have been swallowed by the Sun as it expanded through the red giant phase). Although the future white dwarf Solar System will seem very alien to present day, some things won’t change. Jupiter’s orbit might have receded with the drop in solar mass, it will remain a planetary heavyweight, causing disruption in asteroid orbits. Using known asteroid data, the motion of these chunks of rocks are allowed to evolve, and over millions of years, they may get thrown out of the Solar System, or more interestingly, pushed closer to the white dwarf. Once the whole system has settled down, resonances in the asteroid belt will become amplified; Kirkwood Gaps (caused by gravitational resonance with Jupiter) will widen, and according to Debes’ simulations, the edges of these gaps will become perturbed even more, making more asteroids available to be tidally disrupted and shredded to dust.

Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)

The AAS conference was full of amazing research into white dwarf observations. The reason for this is that there are many white dwarf candidates out there with dusty metallic absorption lines. This means that there used to be rocky bodies orbiting these stars, but became pulverised (by tidal shear) for astronomers to analyse. These white dwarf systems can give us a clue as to what mechanisms could be supplying the white dwarfs with dusty material, even giving us a glimpse into the future of our Solar System.

“We have a physical picture for the link between planetary systems and dusty white dwarfs,” Debes said when describing his model in relation to the mysterious dusty white dwarf observations. “Dusty white dwarfs are truly a mystery! We think we know what might be going on, but we don’t have a smoking gun yet.”

However, Debes is getting close to finding a possible smoking gun, he’s basing his model on some of the key characteristics of these ancient dusty remnants to see what the Solar System could look like in billions of years time.

So, where does this dust come from? As the asteroid orbits are perturbed by Jupiter, they may get close enough to be tidally disrupted. Get too close and they will get shredded by the gravitational shear created by the steep tidal radius of the compact white dwarf. The asteroid dust then settles into the white dwarf. The presence of this dust has a very obvious signature in the absorption lines of spectroscopic data, allowing researchers to infer an accretion rate for metal-rich white dwarfs. In Debes’ model, he has set the upper limit to 10¹⁶ g/year and a lower limit to 10¹³ g/year, consistent with observed estimates.

Spectra of G29-38. Could this resemble the spectra of the Sun after turning into a white dwarf? (NASA/Spitzer)

In his evolved Solar System model, Jupiter’s gravity controls this accretion rate, pushing asteroids toward the white dwarf and, by using a powerful supercomputer to track the perturbations and eventual shredding of known asteroids, there may be an opportunity to arrive at a profound conclusion. Debes is able to use his model to compare observations of known dusty white dwarfs with the simulated outcome of the Solar System. With reference to previous studies (in particularly Koester & Wilken, 2006 in the journal Astronomy & Astrophysics), Debes has found some similar white dwarf “Suns”.

“For G29-38, the canonical dusty white dwarf, they [Koester & Wilken] estimate a total mass of 0.55 solar masses–about what people believe the mass that our own sun will have remaining when it becomes a white dwarf,” Debes added. “But mass estimates are a bit uncertain–I’ve seen estimates ranging from 0.55-0.7 solar masses for this particular white dwarf.”

The Su<span>n's future? The whit</span>e dwarf G29-38 (NASA) — The Sun's future? The white dwarf G29-38 (NASA)

“Another good candidate is a DAZ [a metal-rich white dwarf] called WD 1257+278, which does not show dust but is spot on with the mass expected for the Sun–0.54 M_Sun,” said Debes. “Its accretion rate is also consistent with my model predictions so far assuming an asteroid belt mass and characteristic perturbation timescale that I found in my simulations.”

Debes is continuing to make his model more and more sophisticated, but already the results are promising. Most exciting is that we may already be observing white dwarfs, like G29-38 or WD 1257+278, giving us a tantalizing glimpse of what our Solar System will look like when the Sun becomes a white dwarf star, ripping apart any remaining asteroids and planets as they stray too close to the Sun’s tidal shear. However, it also raises the question: if white dwarfs like G29-38 are being fed by the remains of tidally-blended asteroids, are there massive planets shepherding asteroids in these white dwarf systems too?

March 18, 2009December 24, 2015 by Tammy Plotner

Turning the Tides – NGC 3109 by Ken Crawford

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Somewhere off in the far reaches of Hydra about 4.3 million light years away is a local subgroup of galaxies and a small, barred spiral that just seems to be quietly minding its own business. Or is it? NGC 3109 might not look like much at first, but this little island universe is really turning the tides…

First discovered by John Herschel on March 24, 1835 while in South Africa, NGC 3109 was first classed as an irregular galaxy – the dominating member of a small group of dwarf galaxies believed to be Local Group Member candidates – a determination which isn’t easy to make. “The Local Group dwarf galaxies offer a unique window to the detailed properties of the most common type of galaxy in the Universe.” says Mario L. Mateo, “Our understanding of these galaxies has grown impressively in the past decade, but fundamental puzzles remain that will keep the Local Group at the forefront of galaxy evolution studies for some time.”

What makes NGC 3109 and its little band of followers so interesting? Well, chances are it may not be a member of our Local Group at all, but the nearest of the outsiders. “The small Antlia-Sextans clustering of galaxies is located at a distance of only 1.36 Mpc from the Sun and 1.72 Mpc from the adopted barycenter of the Local Group. The latter value is significantly greater than the radius of the zero-velocity surface of the Local Group that, for an assumed age of 14 Gyr, has R_0=1.18+/-0.15 Mpc.” says Sidney Van den Bergh, “This, together with the observation that the members of the Ant-Sex group have a mean redshift of 114+/-12 km s^-1 relative to the centroid of the Local Group, suggests that the Antlia-Sextans group is not bound to our Local Group and that it is expanding with the Hubble flow. If this conclusion is correct, then Antlia-Sextans may be the nearest external clustering of galaxies.”

So, if NGC 3109 can hold those kind of secrets… What other kinds of secrets can it keep to itself? Try a tiny tidally interacting elliptical galaxy discovered in 1999 by Alan Whiting, George Hau and Mike Irwin. It’s called the Antlia dwarf and it was found to be just beyond the zero-velocity surface of the Local Group. “These data increase the number of certain (or probable) Local Group members to 36. The spatial distribution of these galaxies supports Hubble’s claim that the Local Group “is isolated in the general field.” Currently available evidence suggests that star formation continued much longer in many dwarf spheroidals than it did in the main body of the Galactic halo.” says Sidney Van den Bergh, “It is suggested that “young” globular clusters, such as Ruprecht 106, might have formed in now defunct dwarf spheroidals. Assuming SagDIG, which is the most remote Local Group galaxy, to lie on, or just inside, the zero-velocity surface of the Local Group yields a dynamical age >~17.9+/-2.7 Gyr. However, this value is meaningful only if the outer regions of the local Group are in virial equilibrium.”

Take a look at the full-size image done by Ken Crawford and check out all the red and blue super giant stars and scattered HII regions where new stars are forming – along with all the background galaxies. According to the work of D.G. Barnes; “A substantial warp in the disk of NGC 3109 is detected in the H I emission image in the form of an extended low surface brightness feature. We report a positive detection in H I of the nearby Antlia dwarf galaxy and measure its total neutral gas mass to be 6.8+/-1.4×105 M solar. We show the warp in NGC 3109 to lie at exactly the same radial velocity as the gas in the Antlia dwarf galaxy and speculate that Antlia disturbed the disk of NGC 3109 during a mild encounter ~1 Gyr in the past. H I data for a further eight galaxies detected in the background are presented.”

In the meantime, NGC 3109 continues to be an on-going object of study. Its many compact HII regions could be an indicator of planetary nebulae formations that are totally unlike anything we’ve seen before. “The excitation patterns of the PNe in NGC 3109 are very different from the excitation patterns of PNe in other galaxies.” says Miriam Pena, “This would imply that the evolution of PNe depends upon the properties of their progenitor stellar populations, which vary from galaxy to galaxy. This should affect the PN luminosity function and its use as a distance indicator.” And NGC 3109’s unique structure has equally fascinated Sebastian Hidalgo; “Its edge-on orientation (which simplifies the study of a possible halo) and the possibility that it could, in fact, be a small spiral (the smallest in the Local Group) makes its deep analysis of major relevance to understand the properties of dwarf galaxies and the transition from dwarf irregulars to spirals.”

Many thanks to Ken Crawford for this inspiring image!

March 17, 2009December 24, 2015 by Fraser Cain

Cinder Cone Volcanoes

Cinder cone Paricutin. Image credit: USGS

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Picture a volcano in your mind. You’re probably thinking of a cinder cone volcano, the simplest type of volcano. Cinder cone volcanos have steep sides with a bowl-shaped crater at the top.

Cinder cone volcanoes grow from a single vent in the Earth’s crust. Gas-charged lava is blown violently out of the volcano’s central vent, and the ash and rocks rain down around the vent. After multiple eruptions, the volcano takes on the familiar cone shape, with the erupted rubble forming the steep slopes. Cinder cones rarely grow much taller than 300 meters above their surroundings, and they’re common in western North America, and wherever there’s volcanic activity.

Although they can be solitary structures, cinder cones are often associated with other kinds of volcanoes, like shield volcanoes and stratovolcanoes (or a composite volcano). For example, geologists have discovered more than 100 cinder cones on the sides of Hawaii’s Mauna Kea, one of the biggest volcano in the world. Each cinder cone comes from a vent that opened up on the sides of the volcano.

One of the most famous cinder cone volcanoes erupted out of a Mexican corn field in 1943. The volcano erupted for 9 years, and quickly built up the cinder cone to 424 meters, and covered 25 km² of fields in lava flows and rubble. Nearby towns were eventually buried in ash by the eruptions.

We have written many articles about volcanoes for Universe Today. Here’s an article about the biggest volcano on Earth, and here’s one about the largest volcano in the Solar System.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

March 16, 2009December 24, 2015 by Anne Minard

ESO Image Reveals Galaxy Duo in Explosive Dance

The ‘peculiar galaxy’ Arp 261 has been imaged in unprecedented detail, revealing two galaxies in a slow motion — but highly chaotic and disruptive — close encounter.

Arp 261 lies about 70 million light-years distant in the constellation of Libra, the Scales. The new close-up was captured by the ESO’s Very Large Telescope, at the Paranal Observatory in Chile.

Although individual stars are very unlikely to collide in such an interaction, the huge clouds of gas and dust certainly do crash into each other at high speed, leading to the formation of bright new clusters of very hot stars that are clearly seen in the picture. The paths of the existing stars in the galaxies are also dramatically disrupted, creating the faint swirls extending to the upper left and lower right of the image. Both interacting galaxies were probably dwarfs not unlike the Magellanic Clouds orbiting our own galaxy.

Arp 261 is listed in Halton Arp’s catalogue of Peculiar Galaxies that appeared in the 1960s, with the goal of chronicling objects in the sky that appear strange and may tell rewarding science stories.

The images used to create the new picture of Arp 261 were not actually taken to study the interacting galaxies at all, but to investigate the properties of the inconspicuous object just to the right of the brightest part of Arp 261 and close to the center of the image. This is an unusual exploding star, called SN 1995N, that is thought to be the result of the final collapse of a massive star at the end of its life, a so-called core collapse supernova. SN 1995N is unusual because it has faded very slowly — and still shows clearly more than seven years after the explosion took place.

SN 1995N is also one of the few supernovae to have been observed to emit X-rays. It is thought that these unusual characteristics are a result of the exploding star being in a dense region of space so that the material blasted out from the supernova plows into it and creates X-rays.

Apart from the interacting galaxy and its supernova, the image also contains several other objects at wildly different distances from us. Starting very close to home, two small asteroids, in our Solar System between the orbits of Mars and Jupiter, happened to cross the images as they were being taken and show up as the red-green-blue trails at the left and top of the picture. The trails arise as the objects are moving during the exposures and also between the exposures through different colored filters. The asteroid at the top is number 14670 and the one to the left number 9735. They are probably less than 5 km (3 miles) across. The reflected sunlight from these small bodies takes about 15 minutes to reach Earth.

The next closest object is probably the apparently bright star at the bottom. It may look bright, but it is still about one hundred times too faint to be seen with the unaided eye. It is most likely a star rather like the Sun and about 500 light-years from us — 20 million times further away than the asteroids. Arp 261 itself, and the supernova, are about 140,000 times farther away than this star, but still in what astronomers would regard as our cosmic neighborhood. Much more distant still, perhaps some fifty to one hundred times further away than Arp 261, lies the cluster of galaxies visible on the right of the picture.

Videos of the unusual system are available here and here.

Source: ESO

March 13, 2009December 24, 2015 by Anne Minard

Earth Cyclones, Venus Vortices Have Much in Common

Scientists have spotted an S-shaped feature in the center of the vortices on Venus that looks familiar — because they’ve seen it in tropical cyclones on Earth.

Researchers from the United States and Europe spotted the feature using NASA’s Pioneer Venus Orbiter and The European Space Agency’s Venus Express. Their new discovery confirms that massive, swirling wind patterns have much in common where they have been found — on Venus, Saturn and Earth.

At cloud top level, Venus’ entire atmosphere circles the planet in just about four Earth days, much faster than the solid planet does. Despite this “superrotation,” some dynamical and morphological similarities exist between the vortex organization in the atmospheres of Venus’s northern and southern hemispheres and tropical cyclones and hurricanes on Earth.

Organization of the Venus atmospheric circulation into two circumpolar vortices, one centered on each pole, was first deduced more than 30 years ago from Mariner 10 ultraviolet images. The S-shaped feature in the center of the vortices on Venus was first detected by the Pioneer Venus Orbiter near the northern pole and recently by Venus Express orbiter around the southern pole. It is also known to occur in Earth’s tropical cyclones.

Using an idealized nonlinear and nondivergent barotropic model, lead author Sanjay S. Limaye, of the University of Wisconsin-Madison, and his colleagues are proposing that these S-shaped features are the manifestations of barotropic instability. The feature can be simulated with a barotropic model and, like in the vortices on Venus and in tropical cyclones, it is found to be transient.

Another similarity between the observed features in the vortex circulations of Venus and in terrestrial hurricanes is the presence of transverse waves extending radially outward from the vortex centres. The lack of observations of such features in Earth’s polar vortices is suggestive that the dynamics of the Venus polar vortices may have more in common with hurricanes than their more direct terrestrial counterparts.

Given the challenges in measuring the deep circulation of Venus’s atmosphere, the authors expect that the morphological similarities between vortices on Earth and Venus might help scientists better understand atmospheric superrotation on Venus and guide future observations.

IMAGE CAPTIONS: 1. The ‘eye of the hurricane’ on Venus, taken by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express. The yellow dot represents the south pole. Credit: ESA 2. An infrared satellite image of Hurricane Howard [1998], showing an S-shaped pattern in the low (warm) clouds in the tropical cyclone’s eye. Credit: Sanjay S. Limaye.

Source: Geophysical Research Letters