Death is simply a part of life, and this is no less the case where stars and other astronomical objects are concerned. Sure, the timelines are much, much greater where these are concerned, but the basic rule is the same. Much like all living organism, stars eventually reach old age and become white dwarfs. And some are not even fortunate enough to be born, instead becoming a class of failed stars known as brown dwarfs.
Despite being familiar with these objects, astronomers were certainly not expecting to find examples of both in a single star system! And yet, according to a new study, that is precisely what an international team of astronomers discovered when looked at WD 1202-024. Using data from the Kepler space telescope, they spotted a binary system consisting of a failed star (a brown dwarf) and the remnant of a star (a white dwarf).
It’s been over a century since Einstein firs proposed his Theory of General Relativity, his groundbreaking proposal for how gravity worked on large scales throughout the cosmos. And yet, after all that time, experiments are still being conducted that show that Einstein’s field equations were right on the money. And in some cases, old experiments are finding new uses, helping astronomers to unlock other astronomical mysteries.
Case in point: using the Hubble Space Telescope, NASA astronomers have repeated a century-old test of General Relativity to determine the mass of a white dwarf star. In the past, this test was used to determine how it deflects light from a background star. In this case, it was used to provide new insights into theories about the structure and composition of the burned-out remnants of a star.
White dwarfs are what become of a star after it has exited the Main Sequence of its lifespan after exhausting their nuclear fuel. This is followed by the star expelling most of its outer material, usually through a massive explosion (aka. a supernova). What is left behind is a small and extreme dense (second only to a neutron star) which exerts an incredible gravitational force.
This attribute is what makes white dwarfs a good means for testing General Relativity. By measuring how much they deflect the light from a background star, astronomers are able to see the effect gravity has on the curvature of spacetime. This is precisely similar to what British astronomer Sir Arthur Eddington did in 1919, when he led an expedition to determine how much the Sun’s gravity deflected the light of a background star during a solar eclipse.
Known as gravitational microlensing, this same experiment was repeated by the NASA team. Using the Hubble Space Telescope, they observed Stein 2051B – a white dwarf located just 17 light-years from Earth – on seven different occasions during a two-year period. During this period, it passed in front of a background star located about 5000 light-years distant, which produced a visible deviation in the path of the star’s light.
The resulting deviation was incredibly small – only 2 milliarseconds from its actual position – and was only discernible thanks to the optical resolution of Hubble’s Wide Field Camera 3 (WFC3). Such a deviation would have been impossible to detect using instruments that predate Hubble. And more importantly, the results were consistent with what Einstein predicted a century ago.
As Kailash Sahu, an astronomer at the Space Telescope Science Institute (STScI) and the lead researcher on the project, explained in a NASA press release, this method is also an effective way to test a star’s mass. “This microlensing method is a very independent and direct way to determine the mass of a star,” he said. “It’s like placing the star on a scale: the deflection is analogous to the movement of the needle on the scale.”
The deflection measurement yielded highly-accurate results concerning the mass of the white dwarf star – roughly 68 percent of the Sun’s mass (aka. 0.68 Solar masses) – which was also consistent with theoretical predictions. This is highly significant, in that it opens the door to a new and interesting method for determining the mass of distant stars that do not have companions.
In the past, astronomers have typically determined the mass of stars by observing binary pairs and calculating their orbital motions. Much in the same way that radial velocity measurements are used by astronomers to determine if a planet has a system of exoplanets, measuring the influence two stars have on each other is used to determine how much mass each possesses.
This was how astronomers determined the mass of the Sirius star system, which is located about 8.6 light years from Earth. This binary star system consists of a white supergiant (Sirius A) and a white dwarf companion (Sirius B) which orbit each other with a radial velocity of 5.5 km/s. These measurements helped astronomers determine that Sirius A has a mass of about 2.02 Solar masses while Sirius B weighs in at 0.978 Solar masses.
And while Stein 2051B has a companion (a bright red dwarf), astronomers cannot accurately measure its mass because the stars are too far apart – at least 8 billion km (5 billion mi). Hence, this method could be used in the future wherever companion stars are unavailable or too distant. The Hubble observations also helped the team to independently verify the theory that a white dwarf’s radius can be determined by its mass.
This theory was first proposed by Subrahmanyan Chandrasekhar in 1935, the Indian-American astronomer whose theoretical work on the evolution of stars (and black holes) earned him the Nobel Prize for Physics in 1983. They could also help astronomers to learn more about the internal composition of white dwarfs. But even with an instrument as sophisticated as the WFC3, obtaining these measurements was not without its share of difficulties.
As Jay Anderson, an astronomer with the STScI who led the analysis to precisely measure the positions of stars in the Hubble images, explained:
“Stein 2051B appears 400 times brighter than the distant background star. So measuring the extremely small deflection is like trying to see a firefly move next to a light bulb. The movement of the insect is very small, and the glow of the light bulb makes it difficult to see the insect moving.”
Dr. Sahu presented his team’s findings yesterday (June 7th) at the American Astronomical Society meeting in Austin, Texas. The team’s result will also appear in the journal Science on June 9th. And in the future, the researchers plan to use Hubble to conduct a similar microlensing study on Proxima Centauri, our solar system’s closest stellar neighbor and home to the closest exoplanet to Earth (Proxima b).
It is important to note that this is by no means the only modern experiment that has validated Einstein’s theories. In recent years, General Relativity has been confirmed through observations of rapidly spinning pulsars, 3D simulations of cosmic evolution, and (most importantly) the discovery of gravitational waves. Even in death, Einstein is still making valued contributions to astrophysics!
When we do finally learn the full truth about our place in the galaxy, and we’re invited to join the Galactic Federation of Planets, I’m sure we’ll always be seen as a quaint backwater world orbiting a boring single star.
The terrifying tentacle monsters from the nightmare tentacle world will gurgle horrifying, but clearly condescending comments about how we’ve only got a single star in the Solar System.
The beings of pure energy will remark how only truly enlightened civilizations can come from systems with at least 6 stars, insulting not only humanity, but also the horrifying tentacle monsters, leading to another galaxy spanning conflict.
Yes, we’ll always be making up for our stellar deficit in the eyes of aliens, or whatever those creepy blobs use for eyes.
What we lack in sophistication, however, we make up in volume. In our Milky Way, fully 2/3rds of star systems only have a single star. The last 1/3rd is made up of multiple star systems.
We’re taking binary stars, triple star systems, even exotic 7 star systems. When you mix and match different types of stars in various Odd Couple stellar apartments, the results get interesting.
Consider our own Solar System, where the Sun and planets formed together out a cloud of gas and dust. Gravity collected material into the center of the Solar System, becoming the Sun, while the rest of the disk spun up faster and faster. Eventually our star ignited its fusion furnace, blasting out the rest of the stellar nebula.
But different stellar nebulae can lead to the formation of multiple stars instead. What you get depends on the mass of the cloud, and how fast it’s rotating.
Check out this amazing photograph of a multiple star system forming right now.
In this image, you can see three stars forming together, two at the center, about 60 astronomical units away from each other (60 times the distance from the Earth to the Sun), and then a third orbiting 183 AU away.
It’s estimated these stars are only 10,000 to 20,000 years old. This is one of the most amazing astronomy pictures I ever seen.
When you have two stars, that’s a binary system. If the stars are similar in mass to each other, then they orbit a common point of mass, known as the barycenter. If the stars are different masses, then it can appear that one star is orbiting the other, like a planet going around a star.
When you look up in the sky, many of the single stars you see are actually binary stars, and can be resolved with a pair of binoculars or a small telescope. For example, in a good telescope, Alpha Centauri can be resolved into two equally bright stars, with the much dimmer Proxima Centauri hanging out nearby.
You have to be careful, though, sometimes stars just happen to be beside each other in the sky, but they’re not actually orbiting one another – this is known as an optical binary. It’s a trap.
Astronomers find that you can then get binary stars with a third companion orbiting around them. As long as the third star is far enough away, the whole system can be stable. This is a triple star system.
You can get two sets of binary stars orbiting each other, for a quadruple star system.
In fact, you can build up these combinations of stars up. For example, the star system Nu Scorpii has 7 stars in a single system. All happily orbiting one another for eons.
If stars remained unchanging forever, then this would be the end of our story. However, as we’ve discussed in other articles, stars change over time, bloating up as red giants, detonating as supernovae and turning into bizarre objects, like white dwarfs, neutron stars and even black holes. And when these occur in multiple star systems, well, watch the sparks fly.
There are a nearly infinite combinations you can have here: main sequence, red giant, white dwarf, neutron star, and even black holes. I don’t have time to go through all the combinations, but here are some highlights.
For starters, binary stars can get so close they actually touch each other. This is known as a contact binary, where the two stars actually share material back and forth. But it gets even stranger.
When a main sequence star like our Sun runs out of hydrogen fuel in its core, it expands as a red giant, before cooling and becoming a white dwarf.
When a red giant is in a binary system, the distance and evolution of its stellar companion makes all the difference.
If the two stars are close enough, the red giant can pass material over to the other star. And if the red giant is large enough, it can actually engulf its companion. Imagine our Sun, orbiting within the atmosphere of a red giant star. Needless to say, that’s not healthy for any planets.
An even stranger contact binary happens when a red giant consumes a binary neutron star. This is known as a Thorne-Zytkow object. The neutron star spirals inward through the atmosphere of the red giant. When it reaches the core, it either becomes a black hole, gobbling up the red giant from within, or an even more massive neutron star. This is exceedingly rare, and only one candidate object has ever been observed.
When a binary pair is a white dwarf, the dead remnant of a star like our Sun, then material can transfer to the surface of the white dwarf, causing novae explosions. And if enough material is transferred, the white dwarf explodes as a Type 1A supernova.
If you’re a star that was unlucky enough to be born beside a very massive star, you can actually kicked off into space when it explodes as a supernova. In fact, there are rogue stars which such a kick, they’re on an escape trajectory from the entire galaxy, never to return.
If you have two neutron stars in a binary pair, they release energy in the form of gravitational waves, which causes them to lose momentum and spiral inward. Eventually they collide, becoming a black hole, and detonating with so much energy we can see the explosions billions of light-years away – a short-period gamma ray burst.
The combinations are endless.
It’s amazing to think what the night sky would look like if we were born into a multiple star system. Sometimes there would be several stars in the sky, other times just one. And rarely, there would be an actual night.
How would life be different in a multiple star system? Let me know your thoughts in the comments.
In our next episode, we try to untangle this bizarre paradox. If the Universe is infinite, how did it start out as a singularity? That doesn’t make any sense.
We glossed over it in this episode, but one of the most interesting effects of multiple star systems are novae, explosions of stolen material on the surface of a white dwarf star. Learn more about it in this video.
There are times when I really wish astronomers could take their advanced modern knowledge of the cosmos and then go back and rewrite all the terminology so that they make more sense. For example, dark matter and dark energy seem like they’re linked, and maybe they are, but really, they’re just mysteries.
Is dark matter actually matter, or just a different way that gravity works over long distances? Is dark energy really energy, or is it part of the expansion of space itself. Black holes are neither black, nor holes, but that doesn’t stop people from imagining them as dark tunnels to another Universe. Or the Big Bang, which makes you think of an explosion.
Another category that could really use a re-organizing is the term nova, and all the related objects that share that term: nova, supernova, hypernova, meganova, ultranova. Okay, I made those last couple up.
I guess if you go back to the basics, a nova is a star that momentarily brightens up. And a supernova is a star that momentarily brightens up… to death. But the underlying scenario is totally different.
As we’ve mentioned in many articles already, a supernova commonly occurs when a massive star runs out of fuel in its core, implodes, and then detonates with an enormous explosion. There’s another kind of supernova, but we’ll get to that later.
A plain old regular nova, on the other hand, happens when a white dwarf – the dead remnant of a Sun-like star – absorbs a little too much material from a binary companion. This borrowed hydrogen undergoes fusion, which causes it to brighten up significantly, pumping up to 100,000 times more energy off into space.
Imagine a situation where you’ve got two main sequence stars like our Sun orbiting one another in a tight binary system. Over the course of billions of years, one of the stars runs out of fuel in its core, expands as a red giant, and then contracts back down into a white dwarf. It’s dead.
Some time later, the second star dies, and it expands as a red giant. So now you’ve got a red dwarf and a white dwarf in this binary system, orbiting around and around each other, and material is streaming off the red giant and onto the smaller white dwarf.
This material piles up on the surface of the white dwarf forming a cosy blanket of stolen hydrogen. When the surface temperature reaches 20 million kelvin, the hydrogen begins to fuse, as if it was the core of a star. Metaphorically speaking, its skin catches fire. No, wait, even better. Its skin catches fire and then blasts off into space.
Over the course of a few months, the star brightens significantly in the sky. Sometimes a star that required a telescope before suddenly becomes visible with the unaided eye. And then it slowly fades again, back to its original brightness.
Some stars do this on a regular basis, brightening a few times a century. Others must clearly be on a longer cycle, we’ve only seen them do it once.
Astronomers think there are about 40 novae a year across the Milky Way, and we often see them in other galaxies.
The term “nova” was first coined by the Danish astronomer Tycho Brahe in 1572, when he observed a supernova with his telescope. He called it the “nova stella”, or new star, and the name stuck. Other astronomers used the term to describe any star that brightened up in the sky, before they even really understood the causes.
During a nova event, only about 5% of the material gathered on the white dwarf is actually consumed in the flash of fusion. Some is blasted off into space, and some of the byproducts of fusion pile up on its surface.
Over millions of years, the white dwarf can collect enough material that carbon fusion can occur. At 1.4 times the mass of the Sun, a runaway fusion reaction overtakes the entire white dwarf star, releasing enough energy to detonate it in a matter of seconds.
If a regular nova is a quick flare-up of fusion on the surface of a white dwarf star, then this event is a super nova, where the entire star explodes from a runaway fusion reaction.
You might have guessed, this is known as a Type 1a supernova, and astronomers use these explosions as a way to measure distance in the Universe, because they always explode with the same amount of energy.
Hmm, I guess the terminology isn’t so bad after all: nova is a flare up, and a supernova is a catastrophic flare up to death… that works.
Now you know. A nova occurs when a dead star steals material from a binary companion, and undergoes a momentary return to the good old days of fusion. A Type Ia supernova is that final explosion when a white dwarf has gathered its last meal.
On September 20, a particular spot in the constellation Lupus the Wolf was blank of any stars brighter than 17.5 magnitude. Four nights later, as if by some magic trick, a star bright enough to be seen in binoculars popped into view. While we await official confirmation, the star’s spectrum, its tattle-tale rainbow of light, indicates it’s a nova, a sun in the throes of a thermonuclear explosion.
The nova, dubbed ASASSN-16kt for now, was discovered during the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or “Assassin”), using data from the quadruple 14-cm “Cassius” telescope in CTIO, Chile. Krzysztof Stanek and team reported the new star in Astronomical Telegram #9538. By the evening of September 23 local time, the object had risen to magnitude +9.1, and it’s currently +6.8. So let’s see — that’s about an 11-magnitude jump or a 24,000-fold increase in brightness! And it’s still on the rise.
The star is located at R.A. 15h 29?, –44° 49.7? in the southern constellation Lupus the Wolf. Even at this low declination, the star would clear the southern horizon from places like Chicago and further south, but in late September Lupus is low in the southwestern sky. To see the nova you’ll need a clear horizon in that direction and observe from the far southern U.S. and points south. If you’ve planned a trip to the Caribbean or Hawaii in the coming weeks, your timing couldn’t have been better!
I’ve drawn the map for Key West, one of southernmost locations on the U.S. mainland, where the nova stands about 7-8° high in late twilight, but you might also see it from southern Texas and the bottom of Arizona if you stand on your tippytoes. Other locales include northern Africa, Finding a good horizon is key. Observers across Central and South America, Africa, India, s. Asia and Australia, where the star is higher up in the western sky at nightfall, are favored.
Nova means “new”, but a nova isn’t a brand new star coming to life but rather an explosion that occurs 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 whirling around in a flattened accretion disk around the dwarf, the material gets funneled down to the star’s 150,000 F° surface where gravity compacts and heats the gas until it 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 are relatively rare and almost always found in the plane of the Milky Way, where the stars are most concentrated. The more stars, the greater the chances of finding one in a nova outburst. Roughly a handful a year are discovered, many of those in Scorpius and Sagittarius, in the direction of the galactic bulge.
We’ll keep tabs on this new object and report back with more information and photos as they become available. You can follow the new celebrity as well as print out finder charts on the American Association of Variable Star Observers (AAVSO) website by typing ASASSN-16kt in the info boxes.
I sure wish I wasn’t stuck in Minnesota right now or I’d be staring down the wolf’s new star!
We’ve covered the full range of exotic star-type objects in the Universe. Like Pokemon Go, we’ve collected them all. Okay fine, I’m still looking for a Tauros, and so I’ll continue to wander the streets, like a zombie staring at his phone.
Now, according to my attorney, I’ve fulfilled the requirements for shamelessly jumping on a viral bandwagon by mentioning Pokemon Go and loosely connecting it to whatever completely unrelated topic I was working on.
Any further Pokemon Go references would just be shameless attempts to coopt traffic to my channel, and I’m better than that.
It was pretty convenient, though, and it was easy enough to edit out the references to Quark on Deep Space 9 and replace them with Pokemon Go. Of course, there is a new Star Trek movie out, so maybe I miscalculated.
Anyway, now that we got that out of the way. Back to rare and exotic stellar objects.
There are the white dwarfs, the remnants of stars like our Sun which have passed through the main sequence phase, and now they’re cooling down.
There are the neutron stars and pulsars formed in a moment when stars much more massive than our Sun die in a supernova explosion. Their gravity and density is so great that all the protons and electrons from all the atoms are mashed together. A single teaspoon of neutron star weighs 10 million tons.
And there are the black holes. These form from even more massive supernova explosions, and the gravity and density is so strong they overcome the forces holding atoms themselves together.
White dwarfs, neutron stars and black holes. These were all theorized by physicists, and have all been discovered by observational astronomers. We know they’re out there.
Is that it? Is that all the exotic forms that stars can take? That we know of, yes, however, there are a few even more exotic objects which are still just theoretical. These are the quark stars. But what are they?
Let’s go back to the concept of a neutron star. According to the theories, neutron stars have such intense gravity they crush protons and electrons together into neutrons. The whole star is made of neutrons, inside and out. If you add more mass to the neutron star, you cross this line where it’s too much mass to hold even the neutrons together, and the whole thing collapses into a black hole.
A star like our Sun has layers. The outer convective zone, then the radiative zone, and then the core down in the center, where all the fusion takes place.
Could a neutron star have layers? What’s at the core of the neutron star, compared to the surface?
The idea is that a quark star is an intermediate stage in between neutron stars and black holes. It has too much mass at its core for the neutrons to hold their atomness. But not enough to fully collapse into a black hole.
In these objects, the underlying quarks that form the neutrons are further compressed. “Up” and “down” quarks are squeezed together into “strange” quarks. Since it’s made up of “strange” quarks, physicists call this “strange matter”. Neutron stars are plenty strange, so don’t give it any additional emotional weight just because it’s called strange matter. If they happened to merge into “charm” quarks, then it would be called “charm matter”, and I’d be making Alyssa Milano references.
And like I said, these are still theoretical, but there is some evidence that they might be out there. Astronomers have discovered a class of supernova that give off about 100 times the energy of a regular supernova explosion. Although they could just be mega supernovae, there’s another intriguing possibility.
They might be heavy, unstable neutron stars that exploded a second time, perhaps feeding from a binary companion star. As they hit some limit, they converting from a regular neutron star to one made of strange quarks.
But if quark stars are real, they’re very small. While a regular neutron star is 25 km across, a quark star would only be 16 km across, and this is right at the edge of becoming a black hole.
If quark stars do exist, they probably don’t last long. It’s an intermediate step between a neutron star, and the final black hole configuration. A last gasp of a star as its event horizon forms.
It’s intriguing to think there are other exotic objects out there, formed as matter is compressed into tighter and tighter configurations, as the different limits of physics are reached and then crossed. Astronomers will keep searching for quark stars, and I’ll let you know if they find them.
If you’ve heard me say “oot and aboot”, you know I’m a Canadian. And we Canadians are accustomed to a little cold. Okay, a LOT of cold. It’s not so bad here on the West Coast, but folks from Winnepeg can endure temperatures colder than the surface of Mars. Seriously, who lives like that?
And on one of those cold days, even on a clear sunny day, the Sun is pointless and worthless. As the bone chilling cold numbs your fingers and toes, it’s as if the Sun itself has gone cold, sapping away all the joy and happiness in the world. And don’t get me started about the rain. Clearly, I need to take more tropical vacations.
But we know the Sun isn’t cold at all, it’s just that the atmosphere around you feels cold. The surface of the Sun is always the same balmy 5,500 degrees Celsius. Just to give you perspective, that’s hot enough to melt iron, nickel. Even carbon melts at 2500 C. So, no question, the Sun is hot.
And you know that the Sun is hot because it’s bright. There are actually photons streaming from the Sun at various wavelengths, from radio, infrared, through the visible spectrum, and into the ultraviolet. There are even X-ray photons blasting off the Sun.
If the Sun was cooler, it would look redder, just like a cooler red dwarf star, and if the Sun was hotter, it would appear more blue. But could you have a star that’s cooler, or even downright cold?
The answer is yes, you just have to be willing to expand your definition of what a star is.
Under the normal definition, a star is a collection of hydrogen, helium and other elements that came together by mutual gravity. The intense gravitational pressure of all that mass raised temperatures at the core of the star to the point that hydrogen could be fused into helium. This reaction releases more energy than it takes, which causes the Sun to emit energy.
The coolest possible red dwarf star, one with only 7.5% the mass of the Sun, will still have a temperature of about 2,300 C, a little less than the melting point of carbon.
But if a star doesn’t have enough mass to ignite fusion, it becomes a brown dwarf. It’s heated by the mechanical action of all that mass compressing inward, but it’s cooler. Average brown dwarfs will be about 1,700 C, which actually, is still really hot. Like, molten rock hot.
Brown dwarfs can actually get a lot cooler, a new class of these “stars” were discovered by the WISE Space Observatory that start at 300 degrees, and go all the way down to about 27 degrees, or room temperature. This means there are stars out there that you could touch.
Except you couldn’t, because they’d still have more than a dozen times the mass of Jupiter, and would tear your arm off with their intense gravity. And anyway, they don’t a solid surface. No, you can’t actually touch them.
That’s about as cold as stars get, today, in the Universe.
But if you’re willing to be very very patient, then it’s a different story. Our own Sun will eventually run out of fuel, die and become a white dwarf. It’ll start out hot, but over the eons, it’ll cool down, eventually becoming the same temperature as the background level of the Universe – just a few degrees above absolute zero. Astronomers call these black dwarfs.
We’re talking a long long time, though, in fact, in the 13.8 billion years that the Universe has been around, no white dwarfs have had enough time to cool down significantly. In fact, it would take about a quadrillion years to get within a few degrees of the cosmic microwave background radiation temperature.
Scientists have understood for some time that the most abundant elements in the Universe are simple gases like hydrogen and helium. These make up the vast majority of its observable mass, dwarfing all the heavier elements combined (and by a wide margin). And between the two, helium is the second lightest and second most abundant element, being present in about 24% of observable Universe’s elemental mass.
Whereas we tend to think of Helium as the hilarious gas that does strange things to your voice and allows balloons to float, it is actually a crucial part of our existence. In addition to being a key component of stars, helium is also a major constituent in gas giants. This is due in part to its very high nuclear binding energy, plus the fact that is produced by both nuclear fusion and radioactive decay. And yet, scientists have only been aware of its existence since the late 19th century.
During the late 18th century, Charles Messier began to notice that a series of “nebulous” objects in the night sky that he originally mistook for comets. In time, he would notice that they were in fact something significantly different. With the hope of preventing other astronomers from making the same mistake, he began compiling a list of these in what would come to be known as the Messier Catalog.
Consisting of 100 objects, the catalog became an important milestone in both astronomy and the research of Deep Sky objects. Among the many famous objects in this catalog is the M4 loose globular cluster (aka. NGC 6121). Located in the Scorpius (Scorpio) Constellation, this great cluster of ancient stars is one of the closest Messier Objects of its kind to Earth.