November 19, 2017

Astro-Challenge: Hunting Przybylski’s Star.

Looking south from 28 degrees north an hour after sunset in mid-June.

(Click image for full view; created by the Author in Starry Night).

This week, we turn the astronomical spotlight on a seemingly ordinary star with an extraordinary tale. Often in visual astronomy, simply understanding the amazing facts behind a speck of light at the eyepiece can give it a special significance. Take last week’s transit of Venus, for example. Yes, it was merely a black dot taking almost 7 hours to cross the Sun. Not as splashy or dramatic as a total solar eclipse, sure, but the rarity and the historical significance was part of the fun. Same goes for some previous targets we’ve tracked down in the column, such as white dwarfs and quasars. Sure, you can read the astrophysical journals, but we always like to see this stuff in person. This week, we’d like to introduce you to a star that stubbornly defies astrophysics; Przybylski’s Star.

Located in the constellation Centaurus, this 8th magnitude star just scrapes above the southern horizon about 14 degrees in elevation for northern hemisphere observers around 30° north on June nights about an hour after local sunset. Fans of this site will remember our hunt for another famous Centaurus object, the massive cluster Omega Centauri. Both are visible in late spring/early summer months from mid-to-low northern latitudes, and if you’re around Miami area, you might just be able to nab the northern-most star Gamma Crucis of the Southern Cross asterism in the late spring time as well.

But it’s the non-descript Przybylski’s Star that we’d like to turn your attention (and perhaps your telescope) towards this week. This star is an enigma in terms of its chemistry. It was Antoni Przybylski that first noted the anomalous nature of this star in 1961. About 4 times the mass of our Sun, this star has abnormally low abundances of iron & nickel in its spectra and instead displays high amounts of exotic metals such as uranium, thorium, yttrium and a whole slew of other lanthanides. The fusion process runs out at iron, and all of these heavy elements had to have been forged  in supernovae sometime in the distant past… just what’s going on with Przybylski’s Star? This odd mixture puts the star in a rare category known as an Ap or Bp star, or stars with a high abundance of exotic metals, of which only 35 are known. These stars are well off the main sequence of the Hertzsprung–Russell diagram, and would fall “off the chart” past Delta-Scuti type variables and technetium laden stars. Pryzbylski’s star also displays a mind bogglingly fast pulsation rate of 12 minutes, discovered in 1978.

The star also displays another bizarre trait that may give some clues as to its troubled past; its moving at a slightly higher than usual velocity of about 24 kilometers per second with respect to neighboring stars. To give you some perspective, our own Sun is moving about 20 kilometers per second roughly towards Vega. Could Przybylski’s star have bared witness to several supernovae early in its career, salting it with heavy elements and ejecting it at high velocity? Whatever the case, Przybylski’s star is an astrophysical oddity worth hunting down in the Centaurus region. Its located 6.5° degrees northwest of Delta Centauri and its coordinates are;

Right Ascension: 11h 37’ 37”

Declination: -46° 42’ 35”

Przybylski’s star is about 370 light years distant.

Oh, and the second great mystery (and usually the first question we receive!) is “how the heck to you pronounce Przybylski?” Well, ye ole Internet search turns up a Polish pronunciation of Sh-eh-bel-skEE, though we always welcome a correction on our rusty Polish!

Review: Cowboys & Aliens.

In theaters now!

This weekend, extra-terrestrials invade the Wild West in the Jon Favreau & Steven Spielberg summer sci-fi blockbuster Cowboys & Aliens. If there’s one thing that can unite cowboys, Indians, and western banditos, it’s a good ole fashioned alien invasion. Like many a Spielberg hit, Jaws doesn’t show up until the second reel, in a tale that starts cowboy, but ends alien. We caught this flick on opening day as a way to celebrate 43 orbits around Sol this weekend. Cowboys & Aliens stars a hero of our Sc-fi adventure-laced childhood, Harrison Ford (Indiana Jones, Han Solo) who plays a cattleman and civil war veteran in a down on its luck mining town of Absolution. [Read more...]

February 2011: Life in the Astro-Blogosphere.

The Moon, the ISS, & Jupiter… Van Gogh would be proud! (Photo by Author).

The shortest month of the year is upon us. The month of February brings with it some curious moon alignments, a possible shuttle launch, and some rip roarin’ good Sci-Fi;

Coming to a Sky near You: February 1st kicks off with Jupiter’s moons arranged in 1-2-3-4 visual order. The 3rd sees a good occultation of a bright star by asteroid Irmintraud for the central Florida peninsula (re: Astroguyz HQ), and the 8th sees Saturn’s moons in order. [Read more...]

Death by…Gamma-Ray Burst!


An artist’s impression of a very bad day…(Credit: ESO/A. Roquette).

Sure, we’ve all seen the movies with the impending death by asteroid or comet. You might have even heard of the havoc that can be wrecked by the Sun or an errant black hole, but have you ever heard of death by… gamma ray burst? Very much outside of public consciousness, this was but one of the more exotic ways humanity could have an official bad day that was outlined in Phil Plait’s outstanding Death from the Skies! But what are these exotic beasties, and just how likely are they? [Read more...]

12.06.10: Refurbished Hubble Catches Interstellar Speedster.

Runaway star as seen from the HST. (NASA/ESA/C. Evans/N. Walborn).

Runaway star as seen from the HST. (NASA/ESA/C. Evans/N. Walborn).

 

     New instruments installed aboard the Hubble Space Telescope on the final repair mission are now starting to really show their stuff. Recently, astronomers revealed a new find; a massive star speeding away from the Tarantula Nebula. Located 170,000 light years distant in the Large Magellanic Cloud, this nebula is also sometimes referred to as 30 Doradus or NGC 2070. At the heart of the nebula is a star forming region known as R136. The star in question is speeding outward at an amazing 250,000 mph, or almost 70 miles a second. This would easily span the Earth-Moon distance in one hour! Already, the star has covered about 375 light years in its young estimated 1 to 2 million year long life. What accelerates a star to such a dizzying velocity? One event capable is a nearby supernova explosion. This is unlikely, because any of the siblings within 30 Dor would have been equally young. Another, more likely scenario is that this star had several early encounters with neighboring stars and promptly got flung out of the nebula. 30 Dor boasts several stars in the massive 100+ solar mass category, and is home to some of the largest stars known in the nearby universe.  First indentified in 2006 during a survey conducted at the Siding Spring Observatory in Australia, astronomers got a new view of the stellar runaway when they used it as a calibration target for the newly installed Cosmic Origins Spectrograph. They found a star perhaps 90 times the mass of our Sun unleashing furious stellar winds and carving an enormous bubble in space. COS conducts its observations primarily in the ultraviolet. Observations also confirmed that this star is one single massive entity, and not a close spectroscopic binary. Massive stars such as this are destined for a short life, ending its fusion role as a supernova and eventually leaving a remnant black hole.

21.04.10-The Puzzle of Blue Stragglers.

 

(Credit: NASA/HST).

(Credit: NASA/HST).

 Blue Stragglers as seen by Hubble in the cluster NGC6397.

   Astronomers may have recently solved a half a century long mystery of stellar evolution. Since the 1950’s a type of star known as  a blue straggler has stubbornly refused to fit the Hertzsprung-Russell diagram mold. These older stars should be approaching seniority, but instead burn brightly and spin energetically as if they had somehow gained mass. Most exist in globular or open clusters, and were first identified in the M3 globular cluster. The most well studied example of this stellar sub-class exist in NGC 188, a star cluster about 6,000 light years distant where 21 have been identified. Now, astronomers Robert Mathieu and Aaron Geller of the University of Wisconsin Madison have gained insight into the formation of these elusive beasties and come up with three leading hypotheses;

  1. Matter is accreted from an aging red giant star onto a main sequence companion similar to the process seen in a type IA supernova, but not as massive, causing the star to re-energize;
  2. Two lower mass stars collide, an improbable but not impossible scenario in a densely packed globular cluster;
  3. A third stellar companion perturbs the orbit of a tightly knit binary pair, causing them to merge.

These possibilities were advanced after Mathieu and Geller used observing time on the 3.5-meter WIYN telescope on Kitt Peak spanning the past decade. Studies involved NGC 188, the original “blue straggler” cluster. “These aren’t just normal stars that are straggling behind in their evolution,” stated Mathieu.” There is something unusual going on with their companions.” Computer models would suggest that door number #3 is the most likely candidate; the most logical proof that astronomers would like to have in hand would be to catch a merger in progress.  Interestingly, two known blue stragglers with white dwarf companions lie in the field of the Kepler space telescope, a plus for the accretionary camp. Will we soon have definitive evidence for the origins of these bizarre stars? Or is it perhaps a hybrid of the three models? Stay tuned…

02.04.10- Cassiopeia A: A Quark Star?

Cas A as imaged by Hubble. (Credit: NASA/ESA/ Robert Fesen/James Long).

Cas A as imaged by Hubble. (Credit: NASA/ESA/ Robert Fesen/James Long).

   

   The supernova remnant Cassiopeia A holds a compelling astrophysical mystery. Located about 10,000 light years away, this strong radio source was identified in 1947 and remains the most recent galactic supernova known. One slightly odd fact revolves around Cas A; despite its having burst about 325 years ago as seen from Earth, no reliable records exist of the event. Evidence of the event may have been obscured by intervening galactic dust.  Some intriguing indications show that John Flamsteed may have misidentified the supernova as a sixth magnitude star in Cassiopeia during one of his surveys, but now Cas A may be the home of a even more bizarre denizen; a quark star. This theory stems from the fact that the remnant host appears to be only 10 km across, smaller than your average neutron star. At that density, neutrons loose all individual identity and merge into a huge ball of quark strange matter, a “strange” object indeed. First spotted by the Chandra X-Ray observatory in 1999, this “quark star” would be the first of its kind. Of course, an alternative hypothesis, put forth by Wynn Ho and Craig Heinke of Southampton University, states that we’re merely seeing a normal neutron star of about 25 km in diameter shining through a carbon atom haze. Does astrophysics need to get any weirder?

20.03.10: Spying a Black Hole Welterweight.

An Artist's conception of NGC 5408 X-1. (Credit: NASA).

An Artist's conception of NGC 5408 X-1. (Credit: NASA).

  

   Astronomers now have observational evidence for a missing class of black hole. Stellar mass black holes, those up to about 10 solar masses, are well known as the remnants of supernovae. Likewise for supermassive black holes of 10,000 solar masses or greater known to reside in the hearts of galaxies like our own. The “missing link” in astrophysics has been intermediate mass black holes, or those between 100 and 10,000 solar masses. Now, scientists at the Goddard Space Flight Center in Greenbelt Maryland have used the XMM-Newton and Swift X-ray satellites to pinpoint a likely candidate; NGC 5408 X-1, a black hole with about 1,000 to 9,000 solar masses in a galaxy about 15.8 million light years away in the constellation Centaurus. This would include an event horizon about 3,800 to 34,000 miles across. An X-ray flux occurs once every 115.5 days, strongly suggesting that NGC 5408 X-1 has a stellar companion accreting donor material. This star would be 3-5 times the Sun’s mass.   “Astronomers have been studying NGC 5408 X-1… because it’s one of the best candidates for an intermediate mass black hole.” States Philip Kaaret of the University of Iowa. The contributing companion also gives astronomers the unique opportunity to probe the near-space environment as well as study this intermediate class of enigmatic objects.

Astro-Challenge:When will T Pyxidis Finally Pop?

T Pyxidis; a supernova in the making? (Credit: M. Shara & R. Williams STS, R. Gilmozzi ESO, & NASA)

T Pyxidis; a supernova in the making? (Credit: M. Shara & R. Williams STS, R. Gilmozzi ESO, & NASA)

 

   Earlier this year, the astronomical community was wowed by the eruption of the star U Scorpii. As reported last year in this space, U Sco is a recurrent nova, a flare star that undergoes outburst at irregular intervals. Less than 10 recurrent novae have been identified. The initial action was caught by two Florida based amateurs, and demonstrates that hands on, observational astronomy is still alive and well even in the modern age of astronomical automation. This week, as the waning gibbous moon slides out of the evening sky, I’d like to turn your attention to another of these rare beasts; T Pyxidis. Located in the constellation Pyxis, the Mariner’s Compass, this is one of those unimaginative southern hemisphere constellations thrust upon us in the 18th century. Visually unremarkable, it contains a handful of deep sky objects and clears the horizon sufficiently in the spring evenings for observers in the southern United States to perform routine observations. T Pyxidis itself is a binary system consisting of a white dwarf cannibalizing a sun-like star. When enough in falling matter accumulates, T Pyx flares up from its normal barely detectable magnitude +15.5 to +7.0, almost naked eye visibility. This has happened at roughly 20 year intervals in the years 1890, 1902, 1920, 1944, 1966…and then T Pyx fell silent. We are currently 44 years and counting for an outburst, and this is definitely a star worth continuous scrutiny. The light curve is that of a slow nova, rapidly brightening over a couple of nights, fluctuating at its peak brightness for about a month, and then fading out over proceeding months. T Pyx is a prime candidate for a galactic Type Ia supernova, and at a distance of 3260 light years, could put on quite a show. Of course, said final act could occur tonight, or 10 million years from now; but this current lull makes you think; there has to be a lot of material accreting up there! Its coordinates are;

R.A: 09h 04m 41.5s

Dec: -32 22m 47.5s   

And for an uber-cool finder chart that Sky & Telescope produced a few years back, follow this link… (hint: for use in the field, take the chart and  invert the colors in Paint or Photoshop!)

Good luck, and with a little patience, YOU could be the next amateur to catch T Pyx in the act!

The Astro-term for this week is Chandrasekhar Limit. This is the mass limit of a body in which electron degeneracy pressure can push outward against gravitational collapse. First calculated by Indian astrophysicist Subrahmanyan Chandrasekhar in 1930, this mass is usually given as 1.44 solar masses. Below this limit, a white dwarf and an accompanying planetary nebula will occur; above this mass limit, a core collapse supernova will occur, leaving behind a pulsar or a black hole. T Pyxidis has to be very near its very own Chandrasekhar Limit, with the amount of in-falling mass it is accumulating… will it pop in our lifetime?

06.11.09:A New Type of Supernova?

Astronomers at  the University of California at Berkley may have added a new type of supernova to the list. Typical type I supernovae consist of a carbon-oxygen white dwarf accreting matter from a companion star until a runaway reaction occurs, while type II supernovae involve a collapse of a star perhaps nine times as massive as our Sun. Recently, astronomers uncovered evidence that an extragalactic supernova previously classified as a type II may in fact deserve a class of its own. Named SN 2002bj, this exploding star exhibited the characteristics of a garden variety nova, such as the brief flare up of in-falling hydrogen, but created an explosion 1,000 times more massive. In the case of SN 2002bj, however, the flash also had a conspicuous absence of hydrogen, with instead a strong helium flash and the presence of vanadium in its spectra, a first for a supernova. Theoretical models suggest that this may have been a binary white dwarf pair, with one feeding the other a steady flow of helium until it reached the collapse limit and burst. Also, unlike typical type Ia supernovae, the white dwarf involved survived the explosion. Another unusual signature to this supernova was the way it rapidly faded from sight in about 20 days, about four times faster than usual. SN 2002bj is located in the galaxy NGC 1821 and was spotted in February 2002. Does the classification of supernovae need tweaking?

23.10.09:Fermi Pegs Gamma-Ray Pulsars.

NASA’s Large Area Telescope aboard the orbiting Fermi gamma-ray observatory continues to turn out some amazing science, picking up where Compton left off in 2002 as it surveys the gamma-ray sky. Of particular interest are gamma-rays emitted from pulsars. Pulsars are the swiftly rotating remnants of massive stars that have gone supernova, leaving a superdense core in their wake. These are sometimes called “neutron stars” because the matter comprising them is packed so tightly the individual nuclei are literally stacked end to end, making a spoonful weigh as much as a mountain! After all, most ordinary matter is made of….nothing. A neutron star can be thought of as a large, singular atomic nucleus, again weird stuff. Most of the 1,800 pulsars thus detected are because of their copious radio emissions beaming from their poles. Thus, we have to be in the line of sight before we see their blinking radio pulsations. Enter Fermi, which has thus far spotted 16 new pulsars via their gamma-ray emissions alone. This promises to aid in identifying pulsars whose poles aren’t tipped to our line of sight, which are probably in the majority. But even the gamma-ray sky is relatively dim; for example, the Vela pulsar is one of the brightest in the sky, and it emits a mere 1 gamma-ray photon every 2 minutes! Initially dubbed “Little Green Men” (LGMs!) during their discovery in the 1960′s, pulsars were soon naturally explained, but still continue to amaze. Watch this space and the Fermi mission for news from the high energy end of the spectrum!

Review: Heaven’s Touch by James B. Kaler

Everyone seems to be in a “Death from Above” mood this year. At the happier end of the cosmic spectrum, I give you Heavens Touch, by professor James B. Kaler and out recently courtesy of Princeton Press. Ever wonder were the elemental boron in your laundry cleaner came from? This book will reveal this and other remarkable cosmic secrets. But it’s also a much broader tale, of how the cosmos around us is intertwined with our existence, from the creation of the tides to the precipitation of the elements to the role of cosmic radiation.

[Read more...]

Astro-Event of the Week; 02.06.09: An Antares Occultation.

An occultation of a bright star is well placed for observers in the Americas this weekend. The waning gibbous Moon will occult (i.e. pass in front of) the bright star Antares, also known as Alpha Scorpii. The action begins around 10:00 PM EDT and the Moon will cover up Antares for up to an hour and a half, depending on your latitude. Although the Moon will only be 16 hours away from Full, Antares at about magnitude +1 will be an easy naked eye target, and the skies will be completely dark along East Coast longitudes.

[Read more...]

May 2009 News & Notes.

And the Winner is: It’s official; after much debating and furious blog commenting, the newly discovered moon of the Plutoid Orcus (remember, the anti-Pluto?) is… drum roll… Vanth! Loyal followers of this space and Astronomy Picture of the Day will remember a few weeks ago, when astronomer Mike Brown put out a call to name the tiny object and give a good reason why.

[Read more...]