Amazing New Views of Betelgeuse Courtesy of ALMA

This orange blob is the nearby star Betelgeuse, as imaged recently by the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA/ESO/NRAO

Just. Wow.

An angry monster lurks in the shoulder of the Hunter. We’re talking about the red giant star Betelgeuse, also known as Alpha Orionis in the constellation Orion. Recently, the Atacama Large Millimeter Array (ALMA) gave us an amazing view of Betelgeuse, one of the very few stars that is large enough to be resolved as anything more than a point of light.

Located 650 light years distant, Betelgeuse is destined to live fast, and die young. The star is only eight million years old – young as stars go. Consider, for instance, our own Sun, which has been shining as a Main Sequence star for more than 500 times longer at 4.6 billion years – and already, the star is destined to go supernova at anytime in the next few thousand years or so, again, in a cosmic blink of an eye.

Still lumpy… Betelgeuse imaged by Hubble in 1996. Hubble/ESA/STScI

An estimated 12 times as massive as Sol, Betelgeuse is perhaps a staggering 6 AU or half a billion miles in diameter; plop it down in the center of our solar system, and the star might extend out past the orbit of Jupiter.

As with many astronomical images, the wow factor comes from knowing just what you’re seeing. The orange blob in the image is the hot roiling chromosphere of Betelgeuse, as viewed via ALMA at sub-millimeter wavelengths. Though massive, the star only appears 50 milliarcseconds across as seen from the Earth. To give you some idea just how small a milliarcsecond is, there’s a thousand of them in an arc second, and 60 arc seconds in an arc minute. The average Full Moon is 30 arc minutes across, or 1.8 million milliarcseconds in apparent diameter. Betelgeuse has one of the largest apparent diameters of any star in our night sky, exceeded only by R Doradus at 57 milliarcseconds.

The apparent diameter of Betelgeuse was first measured by Albert Michelson using the Mount Wilson 100-inch in 1920, who obtained an initial value of 240 million miles in diameter, about half the present accepted value, not a bad first attempt.

You can see hints of an asymmetrical bubble roiling across the surface of Betelgeuse in the ALMA image. Betelgeuse rotates once every 8.4 years. What’s going on under that uneasy surface? Infrared surveys show that the star is enveloped in an enormous bow-shock, a powder-keg of a star that will one day provide the Earth with an amazing light show.

The bowshock created by Betelgeuse as it plows through the local interstellar medium. JAXA/Akari

Thankfully, Betelgeuse is well out of the supernova “kill zone” of 25 to 100 light years (depending on the study). Along with Spica at 250 light years distant in the constellation Virgo, both are prime nearby supernovae candidates that will on day give astronomers a chance to study the anatomy of a supernova explosion up close. Riding high to the south in the northern hemisphere nighttime sky in the wintertime, +0.5 magnitude Betelgeuse would most likely flare up to negative magnitudes and would easily be visible in the daytime if it popped off in the Spring or Fall. This time of year in June would be the worst, as Alpha Orionis only lies 15 degrees from the Sun!

An early springtime supernova in the future? Stellarium

Of course, this cosmic spectacle could kick off tomorrow… or thousands of years from now. Maybe, the light of Betelgeuse gone supernova is already on its way now, traversing the 650 light years of open space. Ironically, the last naked eye supernova in our galaxy – Kepler’s Star in the constellation Ophiuchus in 1604 – kicked off just before Galileo first turned his crude telescope towards the heavens in 1610.

You could say we’re due.

What is the Biggest Star in the Universe?

What is the Biggest Star in the Universe

This article was originally published in 2008, but has been updated several times now to keep track with our advancing knowledge of the cosmos!

My six-year old daughter is a question-asking machine. We were driving home from school a couple of days ago, and she was grilling me about the nature of the Universe. One of her zingers was, “What’s the Biggest Star in the Universe”? I had an easy answer. “The Universe is a big place,” I said, “and there’s no way we can possibly know what the biggest star is”. But that’s not a real answer.

So she refined the question. “What’s the biggest star that we know of?” Of course, I was stuck in the car, and without access to the Internet. But once I got back home, and was able to do some research, I learned the answer and thought I’d share it with the rest of you But to answer it fully, some basic background information needs to be covered first. Ready?

Solar Radius and Mass:

When talking about the size of stars, it’s important to first take a look at our own Sun for a sense of scale. Our familiar star is a mighty 1.4 million km across (870,000 miles). That’s such a huge number that it’s hard to get a sense of scale. Speaking of which, the Sun also accounts for 99.9% of all the matter in our Solar System. In fact, you could fit one million planet Earths inside the Sun.

Using these values, astronomers have created the terms “solar radius” and “solar mass”, which they use to compare stars of greater or smaller size and mass to our own. A solar radius is 690,000 km (432,000 miles) and 1 solar mass is 2 x 1030 kilograms (4.3 x 1030 pounds). That’s 2 nonillion kilograms, or 2,000,000,000,000,000,000,000,000,000,000 kg.

Artist's depiction of the Morgan-Keenan spectral diagram, showing the difference between main sequence stars. Credit: Wikipedia Commons
Artist’s depiction of the Morgan-Keenan spectral diagram, showing the difference between main sequence stars. Credit: Wikipedia Commons

Another thing worth considering is the fact that our Sun is pretty small, as stars go. As a G-type main-sequence star (specifically, a G2V star), which is commonly known as a yellow dwarf, its on the smaller end of the size chart (see above). While it is certainly larger than the most common type of star – M-type, or Red Dwarfs – it is itself dwarfed (no pun!) by the likes of blue giants and other spectral classes.

Classification:

To break it all down, stars are grouped based on their essential characteristics, which can be their spectral class (i.e. color), temperature, size, and brightness. The most common method of classification is known as the Morgan–Keenan (MK) system, which classifies stars based on temperature using the letters O, B, A, F, G, K, and M, – O being the hottest and M the coolest. Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g. O1 to M9 are the hottest to coldest stars).

In the MK system, a luminosity class is added using Roman numerals. These are based on the width of certain absorption lines in the star’s spectrum (which vary with the density of the atmosphere), thus distinguishing giant stars from dwarfs. Luminosity classes 0 and I apply to hyper- or supergiants; classes II, III and IV apply to bright, regular giants, and subgiants, respectively; class V is for main-sequence stars; and class VI and VII apply to subdwarfs and dwarf stars.

The Hertzspirg-Russel diagram, showing the relation between star's color, AM. luminosity, and temperature. Credit: astronomy.starrynight.com
The Hertzspirg-Russel diagram, showing the relation between star’s color, AM. luminosity, and temperature. Credit: astronomy.starrynight.com

There is also the Hertzsprung-Russell diagram, which relates stellar classification to absolute magnitude (i.e. intrinsic brightness), luminosity, and surface temperature. The same classification for spectral types are used, ranging from blue and white at one end to red at the other, which is then combined with the stars Absolute Visual Magnitude (expressed as Mv) to place them on a 2-dimensional chart (see above).

On average, stars in the O-range are hotter than other classes, reaching effective temperatures of up to 30,000 K. At the same time, they are also larger and more massive, reaching sizes of over 6 and a half solar radii and up to 16 solar masses. At the lower end, K and M type stars (orange and red dwarfs) tend to be cooler (ranging from 2400 to 5700 K), measuring 0.7 to 0.96 times that of our Sun, and being anywhere from 0.08 to 0.8 as massive.

Based on the full of classification of our Sun (G2V), we can therefore say that it a main-sequence star with a temperature around 5,800K. Now consider another famous star system in our galaxy – Eta Carinae, a system containing at least two stars located around 7500 light-years away in the direction of the constellation Carina. The primary of this system is estimated to be 250 times the size of our Sun, a minimum of 120 solar masses, and a million times as bright – making it one of the biggest and brightest stars ever observed.

Eta Carinae, one of the most massive stars known. Image credit: NASA
Eta Carinae, one of the most massive stars known, located in the Carina constellation. Credit: NASA

There is some controversy over this world’s size though. Most stars blow with a solar wind, losing mass over time. But Eta Carinae is so large that it casts off 500 times the mass of the Earth every year. With so much mass lost, it’s very difficult for astronomers to accurately measure where the star ends, and its stellar wind begins. Also, it is believed that Eta Carinae will explode in the not-too-distant future, and it will be the most spectacular supernovae humans have ever seen.

In terms of sheer mass, the top spot goes to R136a1, a star located in the Large Magellanic Cloud, some 163,000 light-years away. It is believed that this star may contain as much as 315 times the mass of the Sun, which presents a conundrum to astronomers since it was believed that the largest stars could only contain 150 solar masses. The answer to this is that R136a1 was probably formed when several massive stars merged together. Needless to say, R136a1 is set to detonate as a hypernova, any day now.

In terms of large stars, Betelgeuse serves as a good (and popular) example. Located in the shoulder of Orion, this familiar red supergiant has a radius of 950-1200 times the size of the Sun, and would engulf the orbit of Jupiter if placed in our Solar System. In fact, whenever we want to put our Sun’s size into perspective, we often use Betelgeuse to do it (see below)!

Yet, even after we use this hulking Red Giant to put us in our place, we are still just scratching the surface in the game of “who’s the biggest star”. Consider WOH G64, a red supergiant star located in the Large Magellanic Cloud, approximately 168,000 light years from Earth. At 1.540 solar radii in diameter, this star is currently one of the largest in the known universe.

But there’s also RW Cephei, an orange hypergiant star in the constellation Cepheus, located 3,500 light years from Earth and measuring 1,535 solar radii in diameter. Westerlund 1-26 is also pretty huge, a red supergiant (or hypergiant) located within the Westerlund 1 super star cluster 11,500 light-years away that measures 1,530 solar radii in diameter. Meanwhile, V354 Cephei and VX Sagittarii are tied when it comes to size, with both measuring an estimated 1,520 solar radii in diameter.

The Largest Star: UY Scuti

As it stands, the title of the largest star in the Universe (that we know of) comes down to two contenders. For example, UY Scuti is currently at the top of the list. Located 9.500 light years away in the constellation Scutum, this bright red supergiant and pulsating variable star has an estimated average median radius of 1,708 solar radii – or 2.4 billion km (1.5 billion mi; 15.9 AU), thus giving it a volume 5 billion times that of the Sun.

However, this average estimate includes a margin of error of ± 192 solar radii, which means that it could be as large as 1900 solar radii or as small as 1516. This lower estimate places it beneath stars like as V354 Cephei and VX Sagittarii. Meanwhile, the second star on the list of the largest possible stars is NML Cygni, a semiregular variable red hypergiant located in the Cygnus constellation some 5,300 light-years from Earth.

A zoomed-in picture of the red giant star UY Scuti. Credit: Rutherford Observatory/Haktarfone
A zoomed-in picture of the red giant star UY Scuti. Credit: Rutherford Observatory/Haktarfone

Due to the location of this star within a circumstellar nebula, it is heavily obscured by dust extinction. As a result, astronomers estimate that its size could be anywhere from 1,642 to 2,775 solar radii, which means it could either be the largest star in the known Universe (with a margin of 1000 solar radii) or indeed the second largest, ranking not far behind UY Scuti.

And up until a few years ago, the title of biggest star went to VY Canis Majoris; a red hypergiant star in the Canis Major constellation, located about 5,000 light-years from Earth. Back in 2006, professor Roberta Humphrey of the University of Minnesota calculated its upper size and estimated that it could be more than 1,540 times the size of the Sun. Its average estimated mass, however, is 1420, placing it in the no. 8 spot behind V354 Cephei and VX Sagittarii.

These are the biggest star that we know of, but the Milky way probably has dozens of stars that are even larger, obscured by gas and dust so we can’t see them. But even if we cannot find these stars, it is possible to theorize about their likely size and mass. So just how big can stars get? Once again, Professor Roberta Humphreys of the University of Minnesota provided the answer.

VY Canis Majoris. The biggest known star.
Size comparison between the Sun and VY Canis Majoris, which once held the title of the largest known star in the Universe. Credit: Wikipedia Commons/Oona Räisänen

As she explained when contacted, the largest stars in the Universe are the coolest. So even though Eta Carinae is the most luminous star we know of, it’s extremely hot – 25,000 Kelvin – and therefore only 250 solar radii big. The largest stars, in contrast, will be cool supergiants. Case in point, VY Canis Majoris is only 3,500 Kelvin, and a really big star would be even cooler.

At 3,000 Kelvin, Humphreys estimates that cool supergiant would be as big as 2,600 times the size of the Sun. This is below the upper estimates for NML Cygni, but above the average estimates for both it and UY Scutii. Hence, this is the upper limit of a star (at least theoretically and based on all the information we have to date).

But as we continue to peer into the Universe with all of our instruments, and explore it up close through robotic spacecraft and crewed missions, we are sure to find new and exciting things that will confound us further!

And be sure to check out this great animation that shows the size of various objects in space, starting with our Solar System’s tiny planets and finally getting to UY Scuti. Enjoy!

We have written many articles about stars for Universe Today. Here’s The Sun, What’s the Brightest Star in the Sky Past and Future?, and What Is The Smallest Star?

Want to learn more about the birth and death of stars? We did a two part podcast at Astronomy Cast. Here’s part 1, Where Stars Come From, and here’s part 2, How Stars Die.

What Are The Most Famous Stars?

While there are untold billions of celestial objects visible in the nighttime sky, some of them are better known than others. Most of these are stars that are visible to the naked eye and very bright compared to other stellar objects. For this reason, most of them have a long history of being observed and studied by human beings, and most likely occupy an important place in ancient folklore.

So without further ado, here is a sampling of some of the better-known stars in that are visible in the nighttime sky:

Polaris:
Also known as the North Star (as well as the Pole Star, Lodestar, and sometimes Guiding Star), Polaris is the 45th brightest star in the night sky. It is very close to the north celestial pole, which is why it has been used as a navigational tool in the northern hemisphere for centuries. Scientifically speaking, this star is known as Alpha Ursae Minoris because it is the alpha star in the constellation Ursa Minor (the Little Bear).

The Polaris star system, as seen within the Ursa Minor constellation and up close. Credit: NASA, ESA, N. Evans (Harvard-Smithsonian CfA), and H. Bond (STScI)
The Polaris star system, as seen within the Ursa Minor constellation and up close. Credit: NASA, ESA, N. Evans (Harvard-Smithsonian CfA), and H. Bond (STScI)

It’s more than 430 light-years away from Earth, but its luminosity (being a white supergiant) makes it highly visible to us here on Earth. What’s more, rather than being a single supergiant, Polaris is actually a trinary star system, comprised of a main star (alpha UMi Aa) and two smaller companions (alpha UMi B, alpha UMi Ab). These, along with its two distant components (alpha UMi C, alpha UMi D), make it a multistar system.

Interestingly enough, Polaris wasn’t always the north star. That’s because Earth’s axis wobbles over thousands of years and points in different directions. But until such time as Earth’s axis moves farther away from the “Polestar”, it remains our guide.

Because it is what is known as a Cepheid variable star – i.e. a star that pulsates radially, varying in both temperature and diameter to produce brightness changes – it’s distance to our Sun has been the subject of revision. Many scientific papers suggest that it may be up to 30% closer to our Solar System than previously expected – putting it in the vicinity of 238 light years away.

Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King
Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King

Sirius:
Also known as the Dog Star, because it’s the brightest star in Canis Major (the “Big Dog”), Sirius is also the brightest star in the night sky. The name “Sirius” is derived from the Ancient Greek “Seirios“, which translates to “glowing” or “scorcher”. Whereas it appears to be a single bright star to the naked eye, Sirius is actually a binary star system, consisting of a white main-sequence star named Sirius A, and a faint white dwarf companion named Sirius B.

The reason why it is so bright in the sky is due to a combination of its luminosity and distance – at 6.8 light years, it is one of Earth’s nearest neighbors. And in truth, it is actually getting closer. For the next 60,000 years or so, astronomers expect that it will continue to approach our Solar System; at which point, it will begin to recede again.

In ancient Egypt, it was seen as a signal that the flooding of the Nile was close at hand. For the Greeks, the rising of Sirius in the night sky was a sign of the”dog days of summer”. To the Polynesians in the southern hemisphere, it marked the approach of winter and was an important star for navigation around the Pacific Ocean.

Alpha Centauri System:
Also known as Rigel Kent or Toliman, Alpha Centauri is the brightest star in the southern constellation of Centaurus and the third brightest star in the night sky. It is also the closest star system to Earth, at just a shade over four light-years. But much like Sirius and Polaris, it is actually a multistar system, consisting of Alpha Centauri A, B, and Proxima Centauri (aka. Centauri C).

Artist’s impression of the planet around Alpha Centauri B. Credit: ESO
Artist’s impression of the planet around Alpha Centauri B. Credit: ESO

Based on their spectral classifications, Alpha Centauri A is a main sequence white dwarf with roughly 110% of the mass and 151.9% the luminosity of our Sun. Alpha Centauri B is an orange subgiant with 90.7% of the Sun’s mass and 44.5% of its luminosity. Proxima Centauri, the smallest of the three, is a red dwarf roughly 0.12 times the mass of our Sun, and which is the closest of the three to our Solar System.

English explorer Robert Hues was the first European to make a recorded mention of Alpha Centauri, which he did in his 1592 work Tractatus de Globis. In 1689, Jesuit priest and astronomer Jean Richaud confirmed the existence of a second star in the system. Proxima Centauri was discovered in 1915 by Scottish astronomer Robert Innes, Director of the Union Observatory in Johannesburg, South Africa.

In 2012, astronomers discovered an Earth-sized planet around Alpha Centauri B. Known as Alpha Centauri Bb, it’s close proximity to its parent star likely means that it is too hot to support life.

Betelgeuse:
Pronounced “Beetle-juice” (yes, the same as the 1988 Tim Burton movie), this bright red supergiant is roughly 65o light-year from Earth. Also known as Alpha Orionis, it is nevertheless easy to spot in the Orion constellation since it is one of the largest and most luminous stars in the night sky.

Betelgeuse, as seen by the Hubble Space Telescope. Credit: NASA
Betelgeuse, as seen by the Hubble Space Telescope, and in relation to the Orion constellation. Credit: NASA

The star’s name is derived from the Arabic name Ibt al-Jauza’, which literally means “the hand of Orion”. In 1985, Margarita Karovska and colleagues from the Harvard–Smithsonian Center for Astrophysics, announced the discovery of two close companions orbiting Betelgeuse. While this remains unconfirmed, the existence of possible companions remains an intriguing possibility.

What excites astronomers about Betelgeuse is it will one day go supernova, which is sure to be a spectacular event that people on Earth will be able to see. However, the exact date of when that might happen remains unknown.

Rigel:
Also known as Beta Orionis, and located between 700 and 900 light years away, Rigel is the brightest star in the constellation Orion and the seventh brightest star in the night sky. Here too, what appears to be a blue supergiant is actually a multistar system. The primary star (Rigel A) is a blue-white supergiant that is 21 times more massive than our sun, and shines with approximately 120,000 times the luminosity.

Rigel B is itself a binary system, consisting of two main sequence blue-white subdwarf stars. Rigel B is the more massive of the pair, weighing in at 2.5 Solar masses versus Rigel C’s 1.9. Rigel has been recognized as being a binary since at least 1831 when German astronomer F.G.W. Struve first measured it. A fourth star in the system has been proposed, but it is generally considered that this is a misinterpretation of the main star’s variability.

Rigel A is a young star, being only 10 million years old. And given its size, it is expected to go supernova when it reaches the end of its life.

Vega:
Vega is another bright blue star that anchors the otherwise faint Lyra constellation (the Harp). Along with Deneb (from Cygnus) and Altair (from Aquila), it is a part of the Summer Triangle in the Northern hemisphere. It is also the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere (after Arcturus).

Characterized as a white dwarf star, Vega is roughly 2.1 times as massive as our Sun. Together with Arcturus and Sirius, it is one of the most luminous stars in the Sun’s neighborhood. It is a relatively close star at only 25 light-years from Earth.

Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was also one of the first stars whose distance was estimated through parallax measurements, and has served as the baseline for calibrating the photometric brightness scale. Vega’s extensive history of study has led it to be termed “arguably the next most important star in the sky after the Sun.”

Artist's concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega. Credit: NASA/JPL/Caltech/T. Pyle (SSC)
Artist’s concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega. Credit: NASA/JPL/Caltech/T. Pyle (SSC)

Based on observations that showed excess emission of infrared radiation, Vega is believed to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk. For this reason, stars that display an infrared excess because of circumstellar dust are termed “Vega-like stars”.

Thousands of years ago, (ca. 12,000 BCE) Vega was used as the North Star is today, and will be so again around the year 13,727 CE.

Pleiades:
Also known as the “Seven Sisters”, Messier 45 or M45, Pleiades is actually an open star cluster located in the constellation of Taurus. At an average distance of 444 light years from our Sun, it is one of the nearest star clusters to Earth, and the most visible to the naked eye. Though the seven largest stars are the most apparent, the cluster actually consists of over 1,000 confirmed members (along with several unconfirmed binaries).

The core radius of the cluster is about 8 light years across, while it measures some 43 light years at the outer edges. It is dominated by young, hot blue stars, though brown dwarfs – which are just a fraction of the Sun’s mass – are believed to account for 25% of its member stars.

Pleiades by Jamie Ball
Pleiades, also known as M45, is a prominent open star cluster in the sky. Image Credit: Jamie Ball

The age of the cluster has been estimated at between 75 and 150 million years, and it is slowly moving in the direction of the “feet” of what is currently the constellation of Orion. The cluster has had several meanings for many different cultures here on Earth, which include representations in Biblical, ancient Greek, Asian, and traditional Native American folklore.

Antares:
Also known as Alpha Scorpii, Antares is a red supergiant and one of the largest and most luminous observable stars in the nighttime sky. It’s name – which is Greek for “rival to Mars” (aka. Ares) – refers to its reddish appearance, which resembles Mars in some respects. It’s location is also close to the ecliptic, the imaginary band in the sky where the planets, Moon and Sun move.

This supergiant is estimated to be 17 times more massive, 850 times larger in terms of diameter, and 10,000 times more luminous than our Sun. Hence why it can be seen with the naked eye, despite being approximately 550 light-years from Earth. The most recent estimates place its age at 12 million years.

A red supergiant, Antares is about 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Credit: NASA/Ivan Eder
A red supergiant, Antares is over 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Credit: NASA/Ivan Eder

Antares is the seventeenth brightest star that can be seen with the naked eye and the brightest star in the constellation Scorpius. Along with Aldebaran, Regulus, and Fomalhaut, Antares comprises the group known as the ‘Royal stars of Persia’ – four stars that the ancient Persians (circa. 3000 BCE) believed guarded the four districts of the heavens.

Canopus:
Also known as Alpha Carinae, this white giant is the brightest star in the southern constellation of Carina and the second brightest star in the nighttime sky. Located over 300 light-years away from Earth, this star is named after the mythological Canopus, the navigator for king Menelaus of Sparta in The Iliad. 

Thought it was not visible to the ancient Greeks and Romans, the star was known to the ancient Egyptians, as well as the Navajo, Chinese and ancient Indo-Aryan people. In Vedic literature, Canopus is associated with Agastya, a revered sage who is believed to have lived during the 6th or 7th century BCE. To the Chinese, Canopus was known as the “Star of the Old Man”, and was charted by astronomer Yi Xing in 724 CE.

An image of Canopus, as taken by crewmembers aboard the ISS. Credit: NASA
Image of Canopus, as taken by crew members aboard the ISS. Credit: NASA

It is also referred to by its Arabic name Suhayl (Soheil in persian), which was given to it by Islamic scholars in the 7th Century CE. To the Bedouin people of the Negev and Sinai, it was also known as Suhayl, and used along with Polaris as the two principal stars for navigation at night.

It was not until 1592 that it was brought to the attention of European observers, once again by Robert Hues who recorded his observations of it alongside Achernar and Alpha Centauri in his Tractatus de Globis (1592).

As he noted of these three stars, “Now, therefore, there are but three Stars of the first magnitude that I could perceive in all those parts which are never seene here in England. The first of these is that bright Star in the sterne of Argo which they call Canobus. The second is in the end of Eridanus. The third is in the right foote of the Centaure.”

This star is commonly used for spacecraft to orient themselves in space, since it is so bright compared to the stars surrounding it.

Universe Today has articles on what is the North Star and types of stars. Here’s another article about the 10 brightest stars. Astronomy Cast has an episode on famous stars.

Astronomers Find Evidence of a Strange Type of Star

One has never been spotted for sure in the wild jungle of strange stellar objects out there, but astronomers now think they have finally found a theoretical cosmic curiosity: a Thorne-Zytkow Object, or TZO, hiding in the neighboring Small Magellanic Cloud. With the outward appearance of garden-variety red supergiants, TZOs are actually two stars in one: a binary pair where a super-dense neutron star has been absorbed into its less dense supergiant parter, and from within it operates its exotic elemental forge.

First theorized in 1975 by physicist Kip Thorne and astronomer Anna Zytkow, TZOs have proven notoriously difficult to find in real life because of their similarity to red supergiants, like the well-known Betelgeuse at the shoulder of Orion. It’s only through detailed spectroscopy that the particular chemical signatures of a TZO can be identified.

Infrared portrait of the Small Magellanic Cloud, made by NASA's Spitzer Space Telescope
Portrait of the Small Magellanic Cloud, made by NASA’s Spitzer Space Telescope

Observations of the red supergiant HV 2112 in the Small Magellanic Cloud*, a dwarf galaxy located a mere 200,000 light-years away, have revealed these signatures — unusually high concentrations of heavy elements like molybdenum, rubidium, and lithium.

While it’s true that these elements are created inside stars — we are all star-stuff, like Carl Sagan said — they aren’t found in quantity within the atmospheres of lone supergiants. Only by absorbing a much hotter star — such as a neutron star left over from the explosive death of a more massive partner — is the production of such elements presumed to be possible.

“Studying these objects is exciting because it represents a completely new model of how stellar interiors can work,”said Emily Levesque, team leader from the University of Colorado Boulder and lead author on the paper. “In these interiors we also have a new way of producing heavy elements in our universe.”

Definitive detection of a TZO would provide direct evidence for a completely new model of stellar interiors, as well as confirm a theoretically predicted fate for massive star binary systems and the existence of nucleosynthesis environments that offer a new channel for heavy-element and lithium production in our universe.
– E.M. Levesque et al., Discovery of a Thorne-Zytkow object candidate in the Small Magellanic Cloud

One of the original proposers of TZOs, Dr. Anna Zytkow, is glad to see her work resulting in new discoveries.

“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” Zytkow said. “Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time and proceeding with the project.”

The findings were first announced in January at the 223rd meeting of the American Astronomical Society. The paper has now been accepted for publication in the Monthly Notices of the Royal Astronomical Society Letters, and is co-authored by Philip Massey, of Lowell Observatory in Flagstaff, Arizona; Anna Zytkow of the University of Cambridge in the U.K.; and Nidia Morrell of the Carnegie Observatories in La Serena, Chile. Read the team’s paper here.

Source: University of Colorado, Boulder. Illustration by ‘Digital Drew.’
__________________________
*In the paper the team notes that it’s not yet confirmed that HV 2112 is part of the SMC and could be associated with our own galaxy. If so it would rule out it being a TZO, but would still require an explanation of its observed spectra.

Which Star Will Explode Next?

Come on Betelguese, explode already. Or maybe it’ll be Eta Carinae. Which of the billions of stars in the galaxy can we count on to explode next, and when?

When a new supernova is discovered, we can take that as a reminder that we live in a terribly hostile Universe. Sometimes stars just explode, and devastate a corner of a galaxy. On average, a supernova goes off twice a century in a galaxy the size of the Milky Way. Since there are potentially hundreds of billions of galaxies out there, dozens of supernovae are detonating every second in the observable Universe.

The last bright supernova was SN 1987A, located in the Large Magellanic Cloud, about 168,000 light years away. Even though it was far, it exploded with so much energy it was visible to the unaided eye. That one wasn’t even in our galaxy.

The Milky Way’s most recent supernova that we know of was G1.9+0.3, recently confirmed by the Chandra X-Ray Observatory. It would have been visible from Earth about 100 years ago, but it was located in the dusty regions of the Milky Way and obscured from our view.

The last bright supernova was discovered in 1604 by the astronomer Johannes Kepler. This was a naked-eye supernova, in fact, at its peak, it was brighter than any other star in the night sky and for a few weeks it was even visible during the day.

So, which star is likely to explode next? Can we even know that?

Artist’s impression of the supergiant star Betelgeuse as it was revealed with ESO’s Very Large Telescope. Credit: ESO/L.Calçada
Artist’s impression of the supergiant star Betelgeuse as it was revealed with ESO’s Very Large Telescope. Credit: ESO/L.Calçada

We can, and there are even likely candidates. There’s Betelgeuse, the red supergiant star located in the constellation of Orion, only 640 light-years from Earth. Betelgeuse is massive, and it’s only been around for 10 million years. It will likely explode within a million years. Which, in astronomical time, is just before lunch.

Another candidate is Eta Carinae, located about 8,000 light years from us. This blue supergiant has roughly 120 times the mass of the Sun, and it’s ready to explode in the next few hundred thousand years. Which, from the Universe’s perspective is any moment now.

The closest star that could go supernova is most likely Spica, a short 240 light-years from Earth.
Spica has several times the mass of the Sun, it shouldn’t go off for a few million years yet. According to Phil Plait, the Bad Astronomer, another candidate is the star IK Pegasus A at just 150 light-years away.

Bright Star Spica - Brightest Star  in Virgo 16" F4.5   2 minute exposure , 400 ISO
Bright Star Spica – Brightest Star in Virgo by John Chumack

If any of these supernovae do go off, they’ll be incredibly bright. Supernova Betelgeuse would be visible during the day, it might even brighter than the full Moon. It would shine in the sky for weeks, possibly months before fading away.

These explosions are destructive, releasing a torrent of gamma radiation and high energy particles. Fortunately for us, we’re safe. You’d need to be within about 75 light years to really receive a lethal dose. Which means that even the closest supernova candidate is still too far to cause us any real harm.

Which star is set to explode next? Well, in the last second, 30 supernovae just went off, somewhere in the Universe. Here in our galaxy, there should be a supernova in the next 50 years or so, but we still might not be able to see it.
And if we’re really really lucky, Betelgeuse or Eta Carinae will detonate, and we’ll witness one of the most awe inspiring events in the cosmos from the safety of the front porch of our galactic suburban home. Any time now.

Which star would you like to see go supernova? Tell us in the comments below!

The Stars of Orion Seen Blazing From Orbit

The mighty hunter soars above the atmosphere in this photo, taken by NASA astronaut Karen Nyberg currently living and working in space aboard the ISS. One of the most recognizable constellations in night skies all across the Earth, Orion also puts on an impressive display for those well above the Earth!


Appearing here to be lying on his right side, the three stars of Orion’s famous belt — Mintaka, Alnilam, and Alnitak, top to bottom — are center frame, while his sword is nearly horizontal just to the right (the blurry center star of which isn’t a star at all, of course, but rather the enormous star-forming Orion nebula.)

Betelgeuse, as seen by the Hubble Space Telescope.
Betelgeuse, as seen by the Hubble Space Telescope.

At Orion’s right shoulder is Betelgeuse, a huge red giant 20 times more massive than our Sun. Its fiery color is obvious in Karen’s photo, mirroring many of the much-closer human-made city lights visible on the ground.

In addition to featuring my favorite constellation, this photo that Karen recently shared on Twitter also serves to prove (to those few who still require evidence of such) that yes, astronauts can see stars from space. Very nicely too, I may add. The only reason they are not visible in all images is purely photographic — cameras exposing for a bright scene, like a daylit Earth (or Moon) won’t be able to capture the relatively much dimmer light of stars in the same shot, making it look like space is empty of them. Even here we can see a bit of noise in the glowing line of Earth’s atmosphere and a little blurring of edges — that’s a result of a high ISO setting to increase camera sensitivity along with a slightly longer shutter speed than your hand can easily keep stable… again, all to better capture the faint streams of photons from distant stars.

Blaze on, mighty Hunter! See this and more views from the ISS on Karen’s Twitter page here.

Weekly Space Hangout – April 26, 2013

We had an action packed Weekly Space Hangout on Friday, with a vast collection of different stories in astronomy and spaceflight. This week’s panel included Alan Boyle, Dr. Nicole Gugliucci, Scott Lewis, Jason Major, and Dr. Matthew Francis. Hosted by Fraser Cain.

Some of the stories we covered included: Pulsar Provides Confirmation of General Relativity, Meteorites Crashing into Saturn’s Rings, Radio Observations of Betelgeuse, Progress Docks with the ISS, Hubble Observes Comet ISON, Grasshopper Jumps 250 Meters, April 25th Lunar Eclipse, and the Mars One Reality Show.

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern. You can watch us live on Google+, Cosmoquest or listen after as part of the Astronomy Cast podcast feed (audio only).

Weekly Space Hangout – January 25, 2013

Back by popular demand… the Weekly Space Hangout has returned. This is a weekly broadcast on Google+, where I’m joined by a wide and varied team of space and astronomy journalists to discuss the big breaking stories this week.

This week, we talked about:

We record the Weekly Space Hangout every Friday on Google+ at 12:00 pm PST / 3:00 pm EST / 2000 GMT. You’ll want to circle Cosmoquest on Google+ to find out when we’re recording next. The audio for the Weekly Space Hangout is also released to the Astronomy Cast podcast feed.

Unprecedented Images Show Betelgeuse Has Sunspots

Caption:The surface of Betelgeuse in near infrared at 1.64 micron in wavelength, obtained with the IOTA interferometer (Arizona). The image has been re-constructed with two different algorithms, which yield the same details, of 9 milliarcseconds (mas). The star diameter is about 45 milliarcseconds. Credit: Copyright 2010 Haubois / Perrin (LESIA, Observatoire de Paris)

An international team of astronomers has obtained an unprecedented image of the surface of the red supergiant Betelgeuse, in the constellation Orion. The image reveals the presence of two giant bright spots, which cover a large fraction of the surface. Their size is equivalent to the Earth-Sun distance. This observation provides the first strong and direct indication of the presence of the convection phenomenon, transport of heat by moving matter, in a star other than the Sun. This result provides a better understanding of the structure and evolution of supergiants.

Betelgeuse is a red supergiant located in the constellation of Orion, and is quite different from our Sun. First, it is a huge star. If it were the center of our Solar System it would extend to the orbit of Jupiter. At 600 times larger than our Sun, it radiates approximately 100,000 times more energy. Additionally, with an age of only a few million years, the Betelgeuse star is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.

But we now know Betelgeuse has some similarities to the Sun, as it also has sunspots. The surface has bright and dark spots, which are actually regions that are hot and cold spots on the star. The spots appear due to convection, i.e., the transport of heat by matter currents. This phenomenon is observed every day in boiling water. On the surface of the Sun, these spots are rather well-known and visible. However, it is not at all the case for other stars and in particular supergiants. The size, physical characteristics, and lifetime of these dynamical structures remain unknown.

Betelgeuse is a good target for interferometry because its size and brightness make it easier to observe. Using simultaneously the three telescopes of the Infrared Optical Telescope Array (IOTA) interferometer on Mount Hopkins in Arizona (since removed), and the Paris Observatory (LESIA) the astronomers were able to obtain a numerous high-precision measurements. These made it possible to reconstruct an image of the star surface thanks to two algorithms and computer programs.

Two different algorithms gave the same image. One was created by Eric Thiebaut from the Astronomical Research Center of Lyon (CRAL) and the other was developed by Laurent Mugnier and Serge Meimon from ONERA. The final image reveals the star surface with unprecedented, never-before-seen details. Two bright spots clearly show up next to the center of the star.

The analysis of the brightness of the spots shows a variation of 500 degrees compared to the average temperature of the star (3,600 Kelvin). The largest of the two structures has a dimension equivalent
to the quarter of the star diameter (or one and a half the Earth-Sun distance). This marks a clear difference with the Sun where the convection cells are much finer and reach hardly 1/20th of the solar radius (a few Earth radii). These characteristics are compatible with the idea of luminous spots produced by convection. These results constitute a first strong and direct indication of the presence of convection on the surface of a star other than the Sun.

Convection could play an important role in the explanation of the mass-loss phenomenon and in the gigantic plume of gas that is expelled from Betelgeuse. The latter has been discovered by a team led by Pierre Kervella from Paris Observatory (read our article about this discovery). Convection cells are potentially at the origin of the hot gas ejections.

The astronomers say this new discovery provides new insights into supergiant stars, opening up a new field of research.

Sources: Abstract: arXiv, Paper: “Imaging the spotty surface of Betelgeuse in the H band,” 2009, A&A, 508, 923″. Paris Observatory

Betelgeuse

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Betelgeuse is the ninth brightest star in the sky, and the second brightest in the constellation of Orion (it’s the red one, on the opposite side of the Belt from Rigel, which is the blue one, and the brightest).

With a mass of some 20 sols (= the mass of 20 Suns), Betelgeuse is evolving rapidly, even though it’s only a few million years old. It’s now a red supergiant, burning helium in a shell, and (very likely) burning carbon in another shell (closer to the nucleus), and (possibly) oxygen, silicon, and sulfur in other nested shells (like Russian dolls).

Betelgeuse is enormous … if it were where the Sun is, all four inner planets would be inside it! Because it’s so big, and is only approx 640 light-years away, Betelgeuse appears to about 1/20 of an arcsecond in size; this made it an ideal target for optical interferometry. And so it was that in 1920 Michelson and Pease used the 100″ Mt Wilson telescope, with a 20 m interferometer attached to the front, to measure Betelgeuse’s diameter.

The Hubble Space Telescope imaged Betelgeuse directly, in 1995, in the ultraviolet (see above). Why the UV? Because ground-based telescopes can’t make such observations, and because the Hubble’s resolution is greatest in the UV.

Since the 1920s Betelgeuse has been observed, from the ground, by many different optical interferometers, at many wavelengths. Its diameter varies somewhat, as does its brightness (Herschel is perhaps the first astronomer to describe its variability, in 1836). It also has ‘hotspots’, which are ginormous.

Betelgeuse is also shedding mass in giant plumes that stretch to over six times its diameter. Although these plumes will certainly cause it to ‘slim down’, they won’t be enough to stop its core turning to iron (when the silicon there is exhausted, if it hasn’t already done so). Not long afterwards, perhaps within the next thousand years or so, Betelgeuse will go supernova … making it the brightest and most spectacular supernova visible from Earth in perhaps a million years. Fortunately, because we are not looking directly down on its pole, when Betelgeuse does go bang, we won’t be fried by a gamma ray burst (GRB) which may occur (while a core collapse supernova can cause one kind of GRB, it is not yet known if all such supernovae produce GRBs; in any case, such a GRB is one of a pair of jets which rip through the poles of the dying star).

AAVSO has an excellent article on Betelgeuse, and COAST’s (Cambridge Optical Aperture Synthesis Telescope) webpage on its observations of Betelgeuse gives a good summary of one interferometric technique (and some great images too!).

Universe Today has many stories on just about every aspect of Betelgeuse, from its varying size (The Curious Case of the Shrinking Star), the bubbles it’s blowing and its plumes (Closest Ever Look at Betelgeuse Reveals its Fiery Secret), featured in What’s Up This Week, to the bow shock it creates in the interstellar medium (The Bow Shock of Betelgeuse Revealed).

Astronomy Cast’s The Life of Other Stars is a whole episode on the evolution of stars other than the Sun.

References:
http://en.wikipedia.org/wiki/Betelgeuse
http://www.solstation.com/x-objects/betelgeuse.htm