Weekly Space Hangout – May 15, 2015: Finding, Studying and Visiting Other Worlds!

Host: Fraser Cain (@fcain)

Guests:
Jolene Creighton (@jolene723 / fromquarkstoquasars.com)
Brian Koberlein (@briankoberlein / briankoberlein.com)
Dave Dickinson (@astroguyz / www.astroguyz.com)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Alessondra Springmann (@sondy)
Continue reading “Weekly Space Hangout – May 15, 2015: Finding, Studying and Visiting Other Worlds!”

New Binocular Nova Discovered in Sagittarius

This view shows the sky facing south-southeast just before the start of dawn in mid-March from the central U.S. The nova's located squarely in the Teapot constellation. Source: Stellarium

Looks like the Sagittarius Teapot’s got a new whistle. On March 15, John Seach of Chatsworth Island, NSW, Australia discovered a probable nova in the heart of the constellation using a DSLR camera and fast 50mm lens. Checks revealed no bright asteroid or variable star at the location. At the time, the new object glowed at the naked eye limit of magnitude +6, but a more recent observation by Japanese amateur Koichi Itagaki puts the star at magnitude +5.3, indicating it’s still on the rise. 

A 5th magnitude nova’s not too difficult to spot with the naked eye from a dark sky, and binoculars will show it with ease. Make a morning of it by setting up your telescope for a look at Saturn and the nearby double star Graffias (Beta Scorpii), one of the prettiest, low-power doubles in the summer sky.

Close-in map of Sagittarius showing the nova's location (R.A. 18h36m57s Decl. -28°55'42") and neighboring stars with their magnitudes. For clarity, the decimal points are omitted from the magnitudes, which are from the Tycho catalog. Source: Stellarium
Close-in map of Sagittarius showing the nova’s location (R.A. 18h36m57s Decl. -28°55’42”) and neighboring stars with their magnitudes. For clarity, the decimal points are omitted from the magnitudes, which are from the Tycho catalog. Source: Stellarium

Nova means “new”, but novae aren’t fresh stars coming to life but an explosion occurring on the surface of an otherwise faint star no one’s taken notice of – until the blast causes it to brighten 50,000 to 100,000 times. A nova occurs in a close binary star system, where a small but extremely dense and massive (for its size) white dwarf siphons hydrogen gas from its closely orbiting companion. After swirling about in a disk around the dwarf, it’s funneled down to the star’s 150,000 F° surface where gravity compacts and heats the gas until detonates in a titanic thermonuclear explosion. Suddenly, a faint star that wasn’t on anyone’s radar vaults a dozen magnitudes to become a standout “new star”.

Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf pulls material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA
Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf pulls material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA

Regular nova observers may wonder why so many novae are discovered in the Sagittarius-Scorpius Milky Way region. There are so many more stars in the dense star clouds of the Milky Way, compared to say the Big Dipper or Canis Minor, that the odds go up of seeing a relatively rare event like a stellar explosion is likely to happen there than where the stars are scattered thinly. Given this galactic facts of life, that means most of will have to set our alarms to spot this nova. Sagittarius doesn’t rise high enough for a good view until the start of morning twilight. For the central U.S., that’s around 5:45-6 a.m.

A now-you-see-it-now-you-don't animation showing the nova field before and after discovery. Credit: Ernesto Guido and Nick Howes
A now-you-see-it-now-you-don’t animation showing the nova field before and after discovery. Credit: Ernesto Guido and Nick Howes

Find a location with a clear view to the southeast and get oriented at the start of morning twilight or about 100 minutes before sunrise. Using the maps, locate Sagittarius below and to the east (left) of Scorpius. Once you’ve arrived, point your binoculars into the Teapot and star-hop to the nova’s location. I’ve included visual magnitudes of neighboring stars to help you estimate the nova’s brightness and track its changes in the coming days and weeks.

Whether it continues to brighten or soon begins to fade is anyone’s guess at this point. That only makes going out and seeing it yourself that much more enticing.

New photo of Nova Sagittarii. Note the pink color from hydrogen alpha emission. Credit: Erneso Guido and Nick Howes
New photo of Nova Sagittarii. Note the “warm” color from hydrogen alpha emission. Credit: Erneso Guido and Nick Howes

UPDATE: A spectrum of the object was obtained with the Liverpool Telescope March 16 confirming that the “new star” is indeed a nova. Gas has been clocked moving away from the system at more than 6.2 million mph (10 million kph)!

Two Stars On A Death Spiral Set To Detonate As A Supernova

This artist’s impression shows the central part of the planetary nebula Henize 2-428. The core of this unique object consists of two white dwarf stars, each with a mass a little less than that of the Sun. They are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Credit: ESO/L. Calçada

Two white dwarfs circle around one other, locked in a fatal tango. With an intimate orbit and a hefty combined mass, the pair is ultimately destined to collide, merge, and erupt in a titanic explosion: a Type Ia supernova.

Or so goes the theory behind the infamous “standard candles” of cosmology.

Now, in a paper published in today’s issue of Nature, a team of astronomers have announced observational support for such an arrangement – two massive white dwarf stars that appear to be on track for a very explosive demise.

The astronomers were originally studying variations in planetary nebulae, the glowing clouds of gas that red giant stars throw off as they fizzle into white dwarfs. One of their targets was the planetary nebula Henize 2-428, an oddly lopsided specimen that, the team believed, owed its shape to the existence of two central stars, rather than one. After observing the nebula with the ESO’s Very Large Telescope, the astronomers concluded that they were correct – Henize 2-428 did, in fact, have a binary star system at its heart.

This image of the unusual planetary nebula was obtained using ESO’s Very Large Telescope at the Paranal Observatory in Chile. In the heart of this colourful nebula lies a unique object consisting of two white dwarf stars, each with a mass a little less than that of the Sun. These stars are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Credit: ESO
This image of the unusual planetary nebula was obtained using ESO’s Very Large Telescope at the Paranal Observatory in Chile. In the heart of this colourful nebula lies a unique object consisting of two white dwarf stars, each with a mass a little less than that of the Sun. These stars are expected to slowly draw closer to each other and merge in around 700 million years. This event will create a dazzling supernova of Type Ia and destroy both stars. Credit: ESO

“Further observations made with telescopes in the Canary Islands allowed us to determine the orbit of the two stars and deduce both the masses of the two stars and their separation,” said Romano Corradi, a member of the team.

And that is where things get juicy.

In fact, the two stars are whipping around each other once every 4.2 hours, implying a narrow separation that is shrinking with each orbit. Moreover, the system has a combined heft of 1.76 solar masses – larger, by any count, than the restrictive Chandrasekhar limit, the maximum ~1.4 solar masses that a white dwarf can withstand before it detonates. Based on the team’s calculations, Henize 2-428 is likely to be the site of a type Ia supernova within the next 700 million years.

“Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical,” explained David Jones, another of the paper’s coauthors. “The pair of stars in Henize 2-428 is the real thing!”

Check out this simulation, courtesy of the ESO, for a closer look at the fate of the dynamic duo:

 

Astronomers should be able to use the stars of Henize 2-428 to test and refine their models of type Ia supernovae – essential tools that, as lead author Miguel Santander-García emphasized, “are widely used to measure astronomical distances and were key to the discovery that the expansion of the Universe is accelerating due to dark energy.” This system may also enhance scientists’ understanding of the precursors of other irregular planetary nebulae and supernova remnants.

The team’s work was published in the February 9 issue of Nature. A copy of the paper is available here.

End the Year with a Bang! See a Bright Supernova in Virgo

The bright supernova (at tick marks) in the galaxy NGC 4666 photographed on December 24, 2014. Credit: Gregor Krannich

A 14th magnitude supernova discovered in the spiral galaxy NGC 4666 earlier this month has recently brightened to 11th magnitude, making it not only the second brightest supernova of the year, but an easy find in an 8-inch or larger telescope. I made a special trip into the cold this morning for a look and saw it with ease in my 10-inch (25-cm) scope at low power at magnitude 11.9.

Before the Moon taints the dawn sky, you may want to bundle up and have a look, too. The charts below will help you get there.

NGC 4666 is also known as the Superwind Galaxy. Home to vigorous star formation, a combination of supernova explosions and strong winds from massive stars in the starburst region drives a vast outflow of gas from the galaxy into space, a so-called “superwind”. Credit: ESO/J. Dietrich
NGC 4666 is also known as the Superwind Galaxy. Home to vigorous star formation, a combination of supernova explosions and strong winds from massive stars in the starburst region drives a vast outflow of gas from the galaxy into space, called a “superwind”. Credit: ESO/J. Dietrich

With the temporary name ASASSN-14lp, this Type Ia supernova was snatched up by the catchy-titled “Assassin Project”, short for  Automated Sky Survey for SuperNovae (ASAS-SN) on December 9th. Only 80 million light years from Earth, NGC 4666 is a relatively nearby spiral galaxy famous enough to earn a nickname.

Extra-planar soft X-ray emitting hot gas is observed above the most actively star-forming regions in the galactic disk of NGC 4666 and coexists together with filaments of the warm ionized medium, cosmic rays and vertical magnetic field structures channelling (or following) the outflow. Credit: M. Ehle and ESO
Hot, X-ray emitting gas in NGC 4666 billows around the main galaxy as a superwind seen here as outflows on either side of the optical image. Photo taken with the XMM-Newton telescope.  Credit: M. Ehle and ESO

Called the Superwind Galaxy, it’s home to waves of intense star formation thought to be caused by gravitational interactions between it and its neighboring galaxies, including NGC 4668, visible in the lower left corner of the photo above.

Supernovae also play a part in powering the wind which emerges from the galaxy’s central regions like pseudopods on an amoeba.  X-ray and radio light show the outflows best. How fitting that a bright supernova should happen to appear at this time. Seeing one of the key players behind the superwind with our own eyes gives us a visceral feel for the nature of its home galaxy.

Wide view map showing the location of the galaxy NGC 4666 in Virgo not far from Porrima or Gamma Virginis. This map shows the sky facing south shortly before the start of dawn in early January. Source: Stellarium
“Big picture” map showing the location of the galaxy NGC 4666 in Virgo not far from Porrima. The view faces south shortly before the start of dawn in early January. Source: Stellarium

Spectra taken of ASASSN-14lp show it to be a Type Ia object involving the explosive burning of a white dwarf star in a binary system. The Earth-size dwarf packs the gravitational might of a sun-size star and pulls hydrogen gas from the nearby companion down to its surface. Slowly, the dwarf gets heavier and more massive.

When it attains a mass 1.4 times that of the sun, it can no longer support itself. The star suddenly collapses, heats to incredible temperatures and burns up explosively in a runaway fusion reaction. Bang! A supernova.

Detailed map with stars to about magnitude 10. The galaxy is just a little more than a degree northeast of Porrima (Gamma Virginis). Source: Stellarium
Detailed map with stars to about magnitude 10. The galaxy is just a little more than a degree northeast of Porrima (Gamma Virginis). Source: Stellarium

Here are a couple maps to help you find the new object. Fortunately, it’s high in the sky just before the start of dawn in the “Y” of Virgo only a degree or so from the 3rd magnitude double star Porrima, also known as Gamma Virginis. Have at it and let us know if you spot the latest superwind-maker.

For more photos and magnitude updates, check out Dave Bishop’s page on the supernova. You can also print a chart with comparison magnitudes by clicking over to the AAVSO and typing in ASASSN-14lp in the “name” box.

Astro-Challenge: Taming the Pup-Can You Glimpse Sirius B?

White dwarf and companion star resolved.

Astronomy is all about thinking big, both in time and space.

The Earth turns on its axis, the Moon passes through its phases, and the planets come into opposition and solar conjunction on a routine basis.

Of course, on the other end of the spectrum, there are some events which traverse such colossal spans of time that the mere mortal life span of measly homo sapiens such as ourselves can never expect to cover them. Many comets have periods measured in centuries, or thousands of years. The axis of the Earth wobbles like a top, completing one turn every 26,000 years in what’s known as the Precession of the Equinoxes. Our solar system completes one revolution about the galactic center every quarter billion years…

Feeling puny yet? Sure, astronomy is also about humility. But among these stupendous cycles, there are some astronomical events that you just might be able to live through. One such instance is the orbits of double stars. And as 2015 approaches, we challenge you to see of the most famous white dwarf of them all, as it reaches a favorable viewing position over the next few years: Sirius B.

Credit:
Sirius A and B in x-rays courtesy of Chandra. Credit: NASA/SAO/CXC.

Sirius itself is easy to find, as it’s the brightest star in Earth’s sky shining at magnitude -1.42. In fact, you can spot Sirius in the daytime sky if you know exactly where to look.

But it is one of the ultimate in cosmic ironies that the most conspicuous of stars in our sky also hosts such an elusive companion. The discovery of Sirius B awaited the invention of optics capable of resolving it next to its dazzling host. Alvan Clark Jr. and Sr. first spied the enigmatic companion on January 31st, 1862 while testing their newly constructed 18.5 inch refractor, which was the largest at the time. The discovery was soon verified from the Harvard College Observatory, adding Sirius A and B to the growing list of multiple stars.

Photo by the author.
A 19th century refractor similar to the one used to discover Sirius B. Photo by the author.

And what a strange companion it turned out to be. Today, we know that Sirius B is a white dwarf, the cooling dense ember of a main sequence star at the end of its life. We call the matter in such a star degenerate, not as a commentary on its moral stature, but the state the electrons and the closely packed nuclei within under extreme pressure. Our Sun will share the same ultimate fate as Sirius B, about six billion years from now.

Credit
A comparison of a white dwarf (center) and our Sun (right) Credit: RJHall/Wikimedia Commons.

The challenge, should you choose to accept it, is to spot Sirius B in the glare of its host. The contrast in brightness between the pair is daunting: shining at magnitude +11, the B companion is more than 63,000 times fainter than -1.46 magnitude Sirius A.

Created by the author.
The changing position angle of Sirius B. Note that the graphic is inverted, with north at the bottom. Created by the author.

A feat of visual athletics, indeed. Still, Sirius B breaks 10” in separation from its primary in 2015, as it heads towards apastron — its most distant point from its primary, at just over 11” in separation — in 2019. Sirius B varies from 8.2 and 31.5 AUs from its primary. Sirius B is on a 50.1 year orbit, meaning the time to cross this one off of your life list is over the upcoming decade. Perhaps making an animation showing the motion of Sirius B from 2015-2025 would present a supreme challenge as well.

Sirius culminates at local midnight right around New Year’s Eve, shining at its highest to the south as the “ball drops” ushering in 2015. Of course, this is only a fortuitous circumstance that is possible in our current epoch, and precession and the proper motions of both Sirius and Sol will make this less so millennia hence.

Credit: Stellarium.
Sirius crossing the meridian at local midnight on New Year’s Eve. Credit: Stellarium.

Newsflash: there’s a very special visual treat in the offing next week, as comet C/2014 Q2 Lovejoy is currently hovering around +6th magnitude and passes 19 degrees south of Sirius on Christmas Day… more to come!

Magnification and good seeing are your friends in the hunt for Sirius B. Two factors describe the position of a secondary star in a binary pair: its position angle in degrees, and separation in arc seconds. When it comes to stars that are a tough split, I find its better to estimate the position angle first before looking it up. A close match can often confirm the observation. Does a friend see the same thing at the eyepiece? A good star to “warm up” on is the +6.8 magnitude companion to Rigel in the foot of Orion, with a separation of 9”.

Nudging Sirius just out of view might allow the B companion to become apparent. Another nifty star-spliting tool is what’s known as an occulting bar eyepiece. Making an occultation bar eyepiece is easy: we’ve used everything from a small strip of foil to a piece of guitar string (heavy E gauge works nicely) for the central bar. An occulting bar eyepiece is also handy for hunting down the moons of Mars near opposition.

Sirius B also works its way into cultural myths and lore, not the least of which are the curious tales of the Dogon people of Mali. At the outset, it seems that these ancient people have knowledge of a small dense hidden companion star to Sirius, knowledge that requires modern technology to reproduce. Carl Sagan noted, however, that cultural contamination may have resulted in the late 19th century discovery of Sirius B making its way into the Dogon pantheon. The science of anthropology is rife with anecdotes that have been carefully fed to credulous anthropologists only to be reported later as fact, all in the name of a good story.

Credit
A comparison of Sirius B’s real versus apparent trajectory. Credit: SiriusB/Wikimedia Commons.

All amazing things to ponder as you begin your 2015 quest for Sirius B, a bashful but fascinating star.

– Read more on the curious case of the Dogon and Sirius B.

-Want more white dwarfs? Here’s a handy list of white dwarfs of backyard telescopes.

 

 

Possible Bright Supernova Lights Up Spiral Galaxy M61

An animation showing a comparison between the confirmation image (at top) and an archive photo. Credit: Ernesto Guido, Martino Nicolini, Nick Howes

I sat straight up in my seat when I learned of the discovery of a possible new supernova in the bright Virgo galaxy M61. Since bright usually means close, this newly exploding star may soon become visible in smaller telescopes. It was discovered at magnitude +13.6 on October 29th by Koichi Itagaki of Japan, a prolific hunter of supernovae with 94 discoveries or co-discoveries to his credit. Itagaki used a CCD camera and 19.6-inch (0.50-m) reflector to spy the new star within one of the galaxy’s prominent spiral arms. Comparison with earlier photos showed no star at the position. Itagaki also nabbed not one but two earlier supernovae in M61 in December 2008 and November 2006.

The possible supernova in the bright galaxy M61 in Virgo is located 40" east and 7" south of the galaxy's core at right ascension (RA) 12 h 22', declination (Dec) +4º 28' It's currently magnitude +13.4 and visible in the morning sky before dawn in 8-inch and larger telescopes. Credit: Ernesto Guido, Martino Nicolini, Nick Howes
The possible supernova in the bright galaxy M61 in Virgo is located 40″ east and 7″ south of the galaxy’s core at right ascension (RA) 12 h 22′, declination (Dec) +4º 28′. It’s currently magnitude +13.4 and visible in the morning sky before dawn in 8-inch and larger telescopes. Credit: Ernesto Guido, Martino Nicolini, Nick Howes

Overnight, Ernesto Guido and crew used a remote telescope in New Mexico to confirm the new object. We’re still waiting for a spectrum to be absolutely sure this is the real deal and also to determine what type of explosion occurred. In the meantime, it may well brighten in the coming mornings.

M61 is a beautiful barred spiral galaxy located about 55 million light years from Earth in the constellation Virgo. It's one of the few galaxies to show spiral structure in smaller telescopes. Credit: Hunter Wilson
M61 is a beautiful barred spiral galaxy located about 55 million light years from Earth in the constellation Virgo. It’s one of the few galaxies to show spiral structure in smaller telescopes. Credit: Hunter Wilson

Supernovae are divided into two broad categories – Type Ia and Type II. In a Type Ia event,  a planet-sized white dwarf star in close orbit around a normal star siphons off matter from its companion which builds up on the surface of the dwarf until it reaches critical mass at which point the core ignites and consumes itself and the star in one titanic nuclear fusion reaction.  A cataclysmic explosion ensues as the star self-destructs in blaze of glory.

Evolution of a Type Ia supernova. Credit: NASA/ESA/A. Feild
Evolution of a Type Ia supernova. Credit: NASA/ESA/A. Feild

Type Ia explosions can become 5 billion times brighter than the Sun – the reason we can see them across so many light years – and eject matter into space at 5,000 – 20,000 km/second. Type II events mark the end of the life of a massive supergiant star. As these behemoths age, they burn by fusing heavier and heavier elements in their cores from hydrogen to carbon to silicon and finally, iron-nickel. Iron is inert and can’t be cooked or fused to create more energy. The star’s internal heat source, which has been staving back the force of gravity all these millions of years, shuts down.  Gravity takes hold with a vengeance, the star quickly collapses then rebounds in a titanic explosion. Ka-boom! 

Artist's impression of a Type II supernova explosion which involves the destruction of a massive supergiant star. Credit: ESO
Artist’s impression of a Type II supernova explosion which involves the destruction of a massive supergiant star. Credit: ESO

Like the Type Ia event, a Type II supernova grows to fantastic brilliance. Besides a legacy of radiant light, star debris, the creation of heavy elements like gold and lead, a Type II event will sometimes leave behind a tiny, city-sized, rapidly-spinning neutron star – the much compressed core of the original star – or even a black hole. So yes, life can continue for a giant star after a supernova event. But like seeing a former classmate at your 40th high school reunion, you’d hardly recognize it.

The "Y" or cup of Virgo rises into good view shortly before the start of dawn or about 2 hours before sunrise. This map shows the sky facing east around 6 a.m. local time (DST) and 5 a.m. starting Sunday when Daylight Saving Time is done. Source: Stellarium
The “Y” or “cup” of Virgo rises into good view shortly before the start of dawn or about 2 hours before sunrise. This map shows the sky facing east around 6 a.m. local time (DST) tomorrow October 31 and 5 a.m. standard time starting Sunday when Daylight Saving Time ends. Source: Stellarium

Are you itching to see this new supernova for yourself? Here are a couple maps to help you find it. M61 is located in the middle of the “Y” of Virgo not far from the familiar bright double star Gamma Virginis.  From many locations, the galaxy climbs to 15-20° altitude in the east-southeast sky just before the start of dawn, just high enough for a good view. Once you find the galaxy, look for a small “star” superimposed on its eastern spiral arm as shown in the photo at the top of this article.

In this close up view, stars are shown to magnitude +7.5. M61 is right between 16 and 17 Virginis (magnitudes 5 and 6.5 respectively). Source: Stellarium
In this close up view, stars are shown to magnitude +7.5. M61 is right between 16 and 17 Virginis (magnitudes 5 and 6.5 respectively). Click to enlarge.  Source: Stellarium

I’ll be out there with my scope watching and will report back once it’s established what type of supernova happens to be blowing up in our eyepieces. More information about the new object can be found anytime at David Bishop’s Latest Supernovae site. Good luck, clear skies!

** Update Nov. 1 : M61’s supernova now has a name and type! SN 2014dt is a Type Ia (exploding white dwarf) with some peculiarities in its spectrum. It’s also little brighter at magnitude +13.2.

Observing Challenge: 6 White Dwarf Stars to See in Your Backyard Telescope

Dazzlimg Sirius, with its white dwarf companion to the lower left. Credit: NASA, ESA, H. Bond (STScI) and M. Barstow (University of Leicester).

Looking for something off beat to observe? Some examples of curious astronomical objects lie within the reach of the dedicated amateur armed with a moderate-sized backyard telescope. With a little skill and persistence, you just might be able to track down a white dwarf star.  Unlike splashy nebulae or globular clusters, a white dwarf star will just appear as a speck, a tiny dot in the field of view of your telescope’s eyepiece. But just as in the case of observing other exotic objects such as red giants and quasars, part of the thrill of tracking down these astrophysical beasties is in knowing just what it is that you’re seeing. Heck, many amateur astronomers fail to realize that any white dwarf stars are within range of their instruments and have never tracked one down.

The astrophysical nature of white dwarf stars was first uncovered in the early 20th century. Most of the early white dwarf stars discovered were companions in binary star systems and this allowed astronomers to gauge their mass by following the orbital motion of such pairs over time. Soon, astronomers realized that they were looking at something peculiar, a new type of compact but massive stellar object that stubbornly refused to be pigeon-holed along the main sequence of the freshly conceived Hertzsprung-Russell diagram.

Today, we know that white dwarf stars are the remnants of stars which have long since passed the Red Giant stage. We say that a white dwarf is a degenerate star, and no, this not a commentary on its moral state. The Chandrasekhar limit gives us an upper limit in size for a white dwarf at about 1.4 solar masses, beyond which electron degeneracy pressure can no longer act against the inward pull of gravity. Our Sun will one day become a white dwarf, over 6 billion years from now. Think of cramming the mass of our star into the volume of the Earth and you have some idea just how dense a white dwarf is: a cubic centimetre of white dwarf weighs 250 about tons, and two cup fulls of white dwarf would weigh more than a Nimitz-class aircraft carrier.

Think of a white dwarf as a cooling ember of a star long past its hydrogen fusing prime. And white dwarfs will cool down to infrared radiating black dwarfs over trillions of years, far longer than the present 13.7 billion year age of the universe. In fact, the age of white dwarfs currently observed is one on the underpinning tenets of modern Big Bang cosmology.

All amazing stuff. In any event, here is a baker’s half dozen of white dwarf stars that you can find with a telescope tonight. A more extensive list of the nearest white dwarfs to the Earth can be found on Sol Station.

The orbit of Sirius B. Wikimedia Commons image in the Public Domain.
The orbit of Sirius B. Wikimedia Commons image in the Public Domain.

Sirius B:  This is the nearest white dwarf to the Earth at 8.6 light years distant. Shining at magnitude +8.5, Sirius B would be a cinch to see, if only dazzling Sirius A — the brightest star in our sky at magnitude -1.5 — were not nearby. Sirius B orbits its primary once every 50 years and will reach a maximum separation of 11.5” from its primary in 2025, a prime time to cross it off of your life list in the coming decade. Blocking the primary just out of the field of view, or using an occulting bar eyepiece is key to finding Sirius B.

Sirius B was discovered by American telescope maker Alvan Graham Clark in 1862. The Dogon people of Mali also have some curious myths surrounding the star Sirius.

Constellation: Canis Major

Right Ascension: 6 Hours 45’

Declination: -16° 43’

The apparent orbit of Procyon B through 2039. Graphic created by the author.
The apparent orbit of Procyon B through 2039. Graphic created by the author.

Procyon B: Located 11.5 light years distant, Procyon B was discovered in 1896 by John Martin Schaeberle from the Lick observatory. Shining at magnitude +10.7, the chief difficultly with spotting this white dwarf, as with Sirius B, is that it has a companion about 10 magnitudes – that’s 10,000 times brighter – nearby just 4.3” away.

Constellation: Canis Minor

Right Ascension: 7 hours 39’

Declination: +5 13’

Credit: Starry Night Education Software.
The location of GJ 440 (HIP 57367) in the southern sky. Credit: Starry Night Education Software.

-LP145-141: Also known as GJ 440, LP145-141 is one of the best southern hemisphere white dwarf stars on the list. LP145-141 is a solitary white dwarf shining at magnitude +11.5. Located 15 light years distant, LP145-141 is thought to be a member of the nearby Wolf 219 Moving Group of stars.

Constellation: Musca

Right Ascension: 11 Hours 46’

Declination: -64° 50’

Credit: Stellarium
The location of Van Maanen’s Star in the constellation Pisces. Credit: Stellarium

-Van Maanen’s Star: Shining at magnitude +12.4 and located 14.1 light years distant, Van Maanen’s star is the closest solitary white dwarf to Earth and the best example of a white dwarf for small telescopes. Discovered by Ariaan van Maanen in 1917, Van Maanen’s Star also has a very high proper motion of 3” per year.

Constellation: Pisces

Right Ascension: 00 Hours 49’

Declination: 05° 23’

Image by Author
The 40 Omicron Eridani system. Image by Author

-40 Omicron Eridani B: This is a great one to track down. The triple system of 40 Omicron Eridani b contains a fine example of a red and white dwarf orbiting a main sequence star. Located 16.5 light years distant and shining at magnitude +9.5, Omicron Eridani was the first white dwarf star discovered in 1783 by Sir William Herschel, although its true nature wasn’t deduced until 1910. Omicron Eridani B is currently 82” from its primary, an easy split.

Constellation: Eridanus

Right Ascension: 4 Hours 15’

Declination: 7° 39’

-Stein 2051: Rounding off the list and located just over 18 light years distant, Stein 2051 is another example of a red dwarf/white dwarf pair. Stein 2051 b shines at a similar brightest to Van Maanen’s star at magnitude +12.4.

Constellation: Camelopardalis

Right Ascension: 04 Hours 31’

Declination: +58° 59’

Let us know about your trials and triumphs in hunting down these fascinating objects!

An Earth-size Diamond in the Sky: The Coolest Known White Dwarf Detected

Artist impression of a white dwarf star in orbit with pulsar PSR J2222-0137. It may be the coolest and dimmest white dwarf ever identified. Credit: B. Saxton (NRAO/AUI/NSF)

We live in a vast, dark Universe, which makes the smallest and coolest objects extremely difficult to detect, save for a stroke of luck. Often times this luck comes in the form of a companion. Take, for example, the first exoplanet detected due to its orbit around a pulsar — a rapidly spinning neutron star.

A team of researchers using the National Radio Astronomy Observatory’s Green Bank Telescope and the Very Long Baseline Array (VLBA), as well as other observatories have repeated the story, detecting an object in orbit around a distant pulsar. Except this time it’s the coldest, faintest white dwarf ever detected. So cool, in fact, its carbon has crystallized.

The punch line is this: with the help of a pulsar, astronomers have detected an Earth-size diamond in the sky.

“It’s a really remarkable object,” said lead author David Kaplan from the University of Wisconsin-Milwaukee in a press release. “These things should be out there, but because they are so dim they are very hard to find.”

The story begins when Dr. Jason Boyles, then a graduate student at West Virginia University, identified a pulsar, dubbed PSR J2222-0127, 900 light-years away in the constellation Aquarius.

When the core of a massive star runs out of energy, it collapses to form an incredibly dense neutron star or black hole. Bring a teaspoon of neutron star to Earth and it would outweigh Mount Everest at about a billion tons. A pulsar is simply a spinning neutron star.

But as a pulsar spins, lighthouse-like beams of radio waves stream from the poles of its powerful magnetic field. If they sweep past the Earth, they’ll give rise to blips of radio waves, so regular that you could set your watch by them. But if the pulsar carries a companion in tow, the tiny gravitational tugs can offset that timing slightly.

The first observations of PSR J2222-0137 identified that it was spinning more than 30 times each second. It was then observed over a two-year period with the VLBA. By applying Einstein’s theory of relativity — which predicts that light slows in the presence of a gravitational field — the researchers studied how the gravity of the companion warped space, causing delays in the radio signal as the pulsar passed behind it.

The delayed travel times helped the researchers determine the individual masses of the two stars. The pulsar has a mass of 1.2 times that of the Sun and the companion a mass 1.05 times that of the Sun. Previously, researchers had thought the companion was likely another neutron star, or a white dwarf, the remnant of a Sun-like star.

But the timing variations made the neutron star scenario unlikely. The orbits were too orderly for a second supernova to have taken place. So knowing the typical brightness of a white dwarf and its distance, astronomers initially thought they would be able to detect the elusive companion in optical and infrared light.

An image taken in visible light at the SOAR telescope of the field of the pulsar/white dwarf pair. There is no evidence for the white dwarf at the position of the pulsar in this deep image, indicating that the white dwarf is much fainter, and therefore cooler, than any such known object. (The two large white circles mask bright, overexposed stars.)
An image taken in visible light at the SOAR telescope of the field of the pulsar/white dwarf pair. The exact location of the white dwarf is known to a pixel. But it’s not there. Image Credit: NOAO

However, neither the Southern Astrophysical Research telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to detect it.

“Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don’t see a thing,” said coauthor Bart Dunlap, a graduate student at the University of North Carolina. “If there’s a white dwarf there, and there almost certainly is, it must be extremely cold.”

The research team calculated that the white dwarf would be no more than 3,000 degrees Kelvin. At such a low temperature, the collapsed star would be largely crystallized carbon, similar to diamond.

The paper has been accepted for publication in the Astrophysical Journal and may be viewed here.

‘Cosmic Zombie’ Star Triggered This Explosion In Nearby Galaxy

An infrared image of N103B, the remainders of a supernova that exploded about 1,000 years ago in the Large Magellanic Cloud, which is one of the closest galaxies to the Milky Way. Credit: NASA/JPL-Caltech/Goddard

It might be a bad idea to get close to dead stars. Like a White Walker from Game of Thrones, this “cosmic zombie” white dwarf star was dangerous even though it was just a corpse of a star like our own. The result from this violence is still visible in the Spitzer Space Telescope picture you see above.

Astronomers believe the giant star was shedding material (a common phenomenon in older stars), which fell on to the white dwarf star. As the gas built up on the white dwarf over time, the mass became unstable and the dwarf exploded. What’s left is still lying in a pool of gas about 160,000 light-years away from us.

“It’s kind of like being a detective,” stated Brian Williams of NASA’s Goddard Space Flight Center, who led the research. “We look for clues in the remains to try to figure out what happened, even though we weren’t there to see it.”

This explosion in the Large Magellanic Cloud — one of the closest satellite galaxies to Earth — is known as a Type 1a supernova, but it’s a rare breed of that kind. Type 1as are best known as “standard candles” because their explosions have a consistent luminosity. Knowing how luminous the supernova type is allows astronomers to estimate distance based on its apparent brightness; the fainter the supernova is, the further away it is.

Most Type 1as happen when two orbiting white dwarfs smash into each other, but this scenario is more akin to something that Earthlings saw in 1604. Informally called Kepler’s supernova, because it was discovered by astronomer Johannes Kepler, astronomers believe this arose from a red giant and white dwarf interaction. The evidence left for this conclusion showed the supernova leftovers embedded in dust and gas.

Investigators have submitted their results to the Astrophysical Journal.

Source: NASA Jet Propulsion Laboratory

Possible Nova Pops in Cygnus

Cygnus. Credit: Stellarium

A newly-discovered star of magnitude +10.9 has flared to life in the constellation Cygnus the Swan. Koichi Nishiyama and Fujio Kabashima, both of Japan, made their discovery yesterday March 31 with a 105mm f/4 camera lens and electronic camera. They quickly confirmed the observation with additional photos taken with a 0.40-m (16-inch) reflector. Nothing was seen down to magnitude +13.4  in photos taken the on the 27th, but when they checked through images made on March 30 the star present at +12.4. Good news – it’s getting brighter!

This more detailed map, showing stars to mag. 10.5, will help you pinpoint the star. Stellarium
This more detailed map, showing stars to mag. 10.5, will help you pinpoint the star. Its coordinates are R.A. 20h 21m 42, declination +31 o3′. Stellarium

While the possible nova will need confirmation, nova lovers may want to begin observing the star as soon as possible. Novae can brighten quickly, sometimes by several magnitudes in just a day. These maps should help you hone in on the star which rises around midnight and becomes well placed for viewing around 1:30-2 a.m. local time in the eastern sky. At the moment, it will require a 4-inch or larger telescope to see, but I’m crossing my fingers we’ll see it brighten further.

Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf pulls material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA
Novae occur in close binary systems where one star is a tiny but extremely compact white dwarf star. The dwarf pulls material into a disk around itself, some of which is funneled to the surface and ignites in a nova explosion. Credit: NASA

To see a nova is to witness a cataclysm. Astronomers – mostly amateurs – discover about 10 a year in our Milky Way galaxy. Many more would be seen were it not for dust clouds and distance. All involve close binary stars where a tiny but extremely dense white dwarf star steals gas from its companion. The gas ultimately funnels down to the 150,000 degree surface of the dwarf where it’s compacted by gravity and heated to high temperature until it ignites in an explosive fireball. If you’ve ever wondered what a million nuclear warheads would look like detonated all at once, cast your gaze at a nova.

Novae can rise in brightness from 7 to 16 magnitudes, the equivalent of 50,000 to 100,000 times brighter than the sun, in just a few days. Meanwhile the gas they expel in the blast travels away from the binary at up to 2,000 miles per second.

One of the key diagnostics for nova identification is the appearance of deep red light in its spectrum called hydrogen alpha or H-alpha. Italian astronomer obtained this spectrum of the possible nova on April 1. Credit: Gianluca Masi
Emission of deep red light called hydrogen alpha or H-alpha is often diagnostic of a nova. When in the fireball phase, the star is hidden by a fiery cloud of rosy hydrogen gas and expanding debris cloud. Italian astronomer obtained this spectrum of the possible nova on April 1 showing H-alpha emission. Credit: Gianluca Masi

Nishiyama and Kabashima are on something of a hot streak. If confirmed, this would be their third nova discovery in a month! On March 8, they discovered Nova Cephei 2014 at magnitude 11.7 (it’s currently around 12th magnitude) and 10th magnitude Nova Scorpii 2014 (now at around 12.5) on March 26. Impressive.

Photo showing the possible nova in Cygnus. The star is described as being tinted red. Credit: Gianluca Masi
Photo showing the possible nova in Cygnus. The star is described as being tinted red. Credit: Gianluca Masi

Charts for the two older discoveries are available on the AAVSO website. Type in either Nova Cep 2014 or TCP J17154683-3128303 (for Nova Scorpii)  in the Star finder box and click Create a finder chart. I’ll update this article as soon as a chart for the new object is posted.

** UPDATE April 2, 2014: This star has been confirmed as a nova. You can print out a chart by going to the AAVSO website and following the instructions above using Nova Cyg 2014 for the star name. On April 2.4 UT, I observed the nova at magnitude 11.o.