November 24, 2014

Astro-Challenge: Hunting for Van Maanen’s Star.

A Earth-sized star. (Credit: NASA/RXTE).

It’s sobering to ponder the ultimate fate of our Sun. We orbit a middle-aged main sequence star, one that will continue to happily fuse hydrogen into helium for our energy consuming convenience for the next few billion years. We see the ultimate fate of our Sun, however, when we look out at planetary nebulae and burned out cinders known as white dwarfs. [Read more...]

Sirius B and the Curious Case of the Dogon.

The ever-controversial star Sirius. (Photo by Author).

Every beginning astronomy student learns that Sirius is the brightest star in the sky. This brightness is apparent, as Sirius is a spectral type A1V star located relatively close to our solar system at about 8.6 light years away. Much myth and lore surrounds this star, but none is stranger that the mythology of the Dogon people. Incorporated into the mythos of these people that inhabit the plains of Mali is a bizarre tale of Sirius, which they call Sigi Tolo. They claim that the star has a small unseen companion in a 50 year orbit that they call Po Tolo. This companion star is tiny but dense, so dense that all the men in the world could not lift it. The mystery deepens as they also go on to claim that Jupiter has four large moons, and that Saturn has a ring “like that seen sometimes around the Moon, but different…” All of these claims are basically true. Sirius has a companion star, a white dwarf known as Sirius B discovered in 1862 by Alvan Graham Clark. This star is made up of degenerate matter, making it extremely dense, about 1×109 per kg/m^3. And the knowledge of Jupiter and Saturn has been around since Galileo first turned his crude telescope to the heavens…

The Dogon People…

(Credit: Martha de Jong Lantink’s Flickr photostream on a Creative Commons 2.0 License).

So, what’s going on here? Why would an isolated tribe have knowledge that technology only revealed to western eyes in the past few centuries? A quick search around the Internet of the Dogon and Sirius reveals no shortage of theories involving ancient alien contact. The modern pedigree of this tale can be traced back to a 1976 book by Robert Temple entitled The Sirius Mystery. Remember, the 1970’s was a time when Eric von Daniken and his Chariots of the Gods was in vogue, and archeologists were seeing space-helmeted aliens everywhere. Temple based much of his book on the writings of anthropologist Marcel Griaule, who spent time with the Dogon off and on from 1931 to 1956. And much of that particular legend comes from an interview with local Dogon wise man Ogotemmeli. You get the picture. Further research with the Dogon has revealed either no trace of the legend or discrepancies with the tale. For example, they also state that there is a third star in the Sirius system they call Emme ya Tolo, which is the opposite of Po Tolo in that it is both “big and light” but no other star has yet to have been found. Also, as with any sole source, it’s tough to say how much bias there may have been on the part of the recorder… it’s easy to lead a subject, even subconsciously, to the data that we might want to hear. In addition, some confusion exists on whether Ogotemmeli was referring to Sirius or the bright planet Venus in reciting the tale.

The orbit of Sirius B. (Adapted from Burnham’s Celestial Handbook).

In 1979, Carl Sagan proposed that the information might have been given to the Dogon by an external source, albeit a terrestrial one. Keep in mind, the legend coming to light in the 20th century wasn’t really giving us any new information about Sirius; psychics perform this feat all the time when they claim to have predicted events that have already happened. When we look at ancient myths and lore, we need to be mindful of the creativity of the human mind; after all, what would archaeologists thousands of years from now make of a Star Trek episode? That we somehow had warp drive and phaser technology? A true myth having some sort of predictive power would be far more compelling. Does this mean that the discovery of a red dwarf star around Sirius, as was spuriously reported in the 1990’s, would lend some credence to the tale? While interesting, I don’t necessarily believe so, as red/brown dwarf stars are quite common in the cosmos; for example, it’s not totally ruled out that our own sun may have a dim unseen companion!

Like white dwarfs, red dwarfs are common throughout the cosmos. (Credit: NASA/H. Bond).

What Sagan proposed is that the knowledge was passed on by a visiting explorer in the late 19th century, and incorporated into the Dogon mythos by the time Griaule did her interview. The image is compelling; an explorer eager to tell the “primitives” about the triumph of western science, imparting new information to the Dogon about their honored star. Keep in mind, another ancient African people, the Egyptians, based their calendar on the Sothic cycle and the helical rising of the star Sirius. Perhaps, said explorer had a telescope on hand to show them Jupiter and Saturn for good measure.

The original Dogon Sirius diagram. (Credit: Bad Archaeology).

But do any historical expeditions fit the bill? Well, there was in fact a total solar eclipse that passed over the region of modern day Mali on April 16th, 1893, and several expeditions were indeed in the area; these expeditions would have been well-equipped with astronomical gear and astronomy and curiosity about the heavens would have been on the forefront of everyone’s minds. And yes, Saturn had just passed opposition and Jupiter would have been an early evening target in the months leading up to that date.

Jupiter at dusk in April 1893. (Created by the Author in Starry Night).

And the diagram purported to be centuries old? Well, keep in mind that it only bears a passing resemblance to an elliptical orbit; it looks a lot like an egg, which symbolizes re-birth and is prevalent in the mythos of many cultures (witness the “Easter eggs” of western culture; a throwback to pure paganism!) The original diagram sketched out by Ogotemmeli shows several other curious objects within the egg; later commentators have edited them out making the case for Sirius B to seem more conclusive than it really is. And keep in mind that we see the orbit of a binary star system generally tipped to our line of sight between either edge-on and face on; it would relatively easy to find several “matches” to the Dogon diagram in the sky.

The total solar eclipse of 1893. (Credit: Fred Espenak, NASA/GSFC).

While I think the Dogon case is more interesting than most, I don’t find it compelling as a sign of ancient extra-terrestrial contact. Keep in mind, this is still giving us knowledge that we already knew; exacting knowledge, such as a chant that encoded how to build a functioning hyper-drive, for instance, would be much more inexplicable and compelling. The final fact often cited is that the Dogon believe in a heliocentric, or Sun-centered solar system, a fact that took us centuries of denial to realize. In this case, I believe that the Dogon should be recognized as astute observers of the sky; anyone can arrive at this conclusion as the Greeks initially did by merely studying the naked eye motions of the heavens and not allowing pre-conceived notions of how the world should be to cloud their judgment. All too often, we fail to give credit to the ingenuity of ancient cultures where credit is due. These people knew the sky far better than the average citizen does today and relied on it as a natural clock. Perhaps such intimate knowledge of peoples like the Dogon should be viewed for what it really is, rather than attributed as merely given to them from afar.

Review: How Old is the Universe? By David A. Weintraub.

Out from Princeton Press.

Probably the toughest questions an astronomer ever has to field with the public are those in cosmology. How old/how big/how far are truly mind bending questions, and difficult to explain to the average man on the street in sound-bite style. This week, we look at David Weintraub’s latest, How Old is the Universe? out by Princeton Press. Fans of this site will remember our review of Is Pluto a Planet? also by Mr. Weintraub a few years back. [Read more...]

03.06.10: Do “Dirty” White Dwarfs Provide a Key Spectral Signature?

 

White dwarf stars as seen by the Hubble Space Telescope dotting the globular cluster M4. (Credit: NASA/H. Richer).

White dwarf stars as seen by the Hubble Space Telescope dotting the globular cluster M4. (Credit: NASA/H. Richer).

 

   If astronomers at the Leicester University in the United Kingdom are correct, the key elements and chemicals that comprise life may be common throughout our Milky Way. The evidence comes from an unlikely source; spectral examinations of populations of galactic white dwarfs. These ancient remnants of stars exist in vast numbers, and our Sun will indeed share their fate one day. The study, led by researcher Jay Farihi, looked at over 100 million objects in the Sloan Digital Sky Survey, which provides a map of the sky and our galaxy as seen in the infrared spectrum. Their findings conclude that up to 20% of all white dwarfs surveyed are contaminated with trace metals, most likely the result of interplanetary debris. In the field of astronomy, the term “metal” refers to anything that isn’t hydrogen or helium, a little different definition than what you learned (hopefully) in high school chemistry. The thinking goes that where heavier elements are seen, terrestrial planets and perhaps life may be sure to follow. Our Sun itself is a good case in point; a Population I star that is relatively metal rich, allowing for a large retinue of rocky planets, including the Earth. How common or rare we are is still hotly debated, but this analysis of the atmospheres of white dwarfs may prove that terrestrial worlds are perhaps abundant throughout the cosmos.  In terms of this study, astronomers are in a sense looking at the “ruins” of older terrestrial systems that will be recycled and incorporated into new, metal dense populations… perhaps one could argue that as time in universe marches on and heavier elements become more abundant, the odds are that life will become more frequent, at least until the stelliferous era runs its course!

15.05.10: A Speedy Binary.

 

  An artist's concpetion of HM Cancri. (Credit: NASA).

  

   Think that new Ducati in your garage is fast? Let me introduce you to HM Cancri. An unassuming +21 magnitude binary in the constellation Cancer, HM Cancri is comprised of two white dwarfs locked in a tight embrace. In fact, this binary system has the shortest orbital period known, handily knocking down distant contender V407 Vulpeculae with its “stately” 9.5 minute orbit. The facts are dizzying; the pair weigh in at 0.5 and 0.25 solar masses respectively, are about 24,000 miles apart (think geosynchronous orbit!) and revolve around each other in 5.4 minutes, about the time you hopefully spend glancing over this blog before returning to Facebook.  Get your calculators out; this makes orbital velocity for the pair an impressive 230 miles per second! Discovered in 1999, Observations using the Keck telescope have upheld HM Cancri’s record holding status by analyzing opposing spectral shifts of ionized helium as the two stars whirl about. This rules out other candidates such as a single neutron star.  Such a system must have had a very unique history, perhaps starting as a pair of Sun-like stars that later spiraled in. Will the two merge one day? Conservation of angular momentum cannot fully explain what we see as the system is speeding up; perhaps more accreting matter is present than we currently account for. The pair are approaching each other by about two feet per day, and of course, relativity comes into play in such an extreme system. Clearly, something interesting is occurring in this system. HM Cancri is also a strong x-ray source, and should generate copious amounts of gravity waves, especially in the event of a merger. Said waves may be within the realm of Advanced LIGO, due to come online in 2014, or LISA, ESA’s proposed Laser Interferometer Space Antenna. HM Cancri lies about 16,000 light years distant, and may be the strongest source of gravity waves in our galaxy.

12.05.10- White Dwarf Lite?

 

A comparison of Kepler's latest planetary finds. (Graphic Credit: NASA).

A comparison of Kepler's latest planetary finds. (Graphic Credit: NASA).

 

   The Kepler space telescope may have bagged an unexpected prize during its hunt for exo-planets. Along with five published exoplanets illustrated above, Kepler snared two potentially bizarre objects. Dubbed KOI (Kepler Objects of Interest) -81 and 74, these companions actually appear dimmer passing behind the parent star rather than in front of it. This suggests a bright luminous object(s) with an Earth-like diameter but much more massive… a white dwarf? Possibly, but the objects seem to be physically too large to fit this class of objects. White dwarfs have an upper limit of about 1.4 solar masses, also known famously as the Chandrasekhar limit. Recently, scientist Jason Rowe of NASA Ames research center has been able to directly measure the masses of these companions by measuring the way the companions physically warp, or distort the bodies of their primary companions. The result; these stars are in the realm of 0.1 solar masses, which would make them some the lightest white dwarfs known. Obviously, this also becomes a problem because although small and luminous, KOI-81 and -74 probably aren’t supported solely by electron degeneracy pressure that characterizes standard classical white dwarfs. The situation just got stranger and stranger… were these objects large super-heated planets or light white dwarfs?

Enter an international team of astronomers meeting at Kavli Institute in Peking (Beijing) China. Using an innovative technique known as Doppler boosting, they were able to pinpoint the mystery objects mass at 0.2 solar masses, on the low end but still in the realm of a white dwarf. This makes even more sense if one considers a white dwarf accreting mass from a primary companion, ala a Type 1A supernovae candidate…(hey, didn’t we write in this space last week about the lack of these beasties?)   Doppler boosting works in terms of catching subtle fluctuations in the brightening of an approaching object as measured by photons received over a given unit of time and dimming as it recedes…altogether a complicated affair, considering this must be untangled from a flurry of other signals. This unexpected find illustrates that surreptitious discoveries are often the norm in astronomy, if only someone is willing to look for them!

Astro-Event of the Week-Redder than Red: V Hydrae.

(Created in Starry Night and Paint).

(Created in Starry Night and Paint).

 V Hydrae finder chart.

   This week, we here at Astroguyz are going to introduce you to a star that isn’t on the top 10 star party faves, but perhaps should be; V Hydrae. [Read more...]

15.04.10- Do We Know the Future of our Sun?

(Credit: Oliver Beatson).

(Credit: Oliver Beatson).

  You Are Here!

    Our modern understanding of stellar evolution states that our Sun is a middle-aged main sequence star, destined to bellow up into a Red Giant in a few billion years and eventually wind up as a degenerate white dwarf embedded in a shroud of a planetary nebula. Looking out at the stars in various stages of evolution in our galaxy, we see systems that have done just that. These Red Giants often exhibit a rhythmic oscillation as their atmospheres swell and contract, but about one third also display a longer five year variation that scientists do not completely understand. Now, a study conducted by the European Southern Observatories’ Very Large Telescope (VLT) is looking into this mystery by studying 58 sun-like stars towards their elderly Red Giant stage located in the Large Magellanic Cloud. Known since the 1930’s, this mystery has baffled astronomers. “Astronomers are left in the dark, and for once, we do not enjoy it,” stated Christine Nicholls of Australia’s Mount Stromlo Observatory. Some of the long term pulsations could be explained by the presence of an unseen binary companion, but not all. This phenomenon is of special interest to astrophysicists because our own Sun may one day throw similar temper tantrums. Could stellar evolution be in need of tweaking?

Astro-Challenge:Spy a White Dwarf!

Can you see Vulcan? (Photo by Author).

Can you see Vulcan? (Photo by Author).

This week, I’m going to introduce you to a unique but fascinating multiple star system, and one that’s definitely worth seeking out as it’s a good study in comparative stellar evolution; Omicron Eridani. This one will require a telescope of about 4′ aperture or greater, a go-to scope or a good finder chart, and patience. But the quarry is worth it; for Omicron Eridanus B is a white dwarf, the most easily observable in the sky, paired with C, a red dwarf star! Omicron Eridani is a triple star system, about 16.5 light years distant. The primary star, a K type main sequence star, is visible to the naked eye at a magnitude of about +4.5. Known to the Arabs as Al Keid (“the Egg”), [Read more...]

06.11.09:A New Type of Supernova?

Discovery image of SN 2002bj. (Credit: U of C Berkeley).

Discovery image of SN 2002bj. (Credit: U of C Berkeley).

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?

14.9.9:U Scorpii:A Nova in Waiting?

A Cataclysmic Variable Star. (Image credit & copyright Mark A. Garlick and has been used with permission. Please do not use this image in any way whatsoever without first contacting the artist).

A Cataclysmic Variable Star.

(Image credit & copyright courtesy of Mark A. Garlick; used by permission.

Please do not use this image in any way whatsoever without first contacting the artist).

Recurrent novae are among the rarest of beasts. While one-off galactic nova come and go throughout the year, recurrent novae are among those very few stars that have been known to exhibit nova-like flares multiple times. This week, I turn your attention towards U Scorpii, a known recurrent nova in the head of the constellation Scorpius. As the bright Moon is currently out of the evening sky, now and next month is the time to peek at this unique star before it slides behind the Sun. First discovered in 1863 by English astronomer N.R. Pogson during an outburst, U Scorpii stands as one of the fastest recurrent nova known, [Read more...]