Hubble Frontier Fields observing programme, which is using the magnifying power of enormous galaxy clusters to peer deep into the distant Universe. Credit: NASA.
Gravity’s a funny thing. Not only does it tug away at you, me, planets, moons and stars, but it can even bend light itself. And once you’re bending light, well, you’ve got yourself a telescope.
Everyone here is familiar with the practical applications of gravity. If not just from exposure to Loony Tunes, with an abundance of scenes with an anthropomorphized coyote being hurled at the ground from gravitational acceleration, giant rocks plummeting to a spot inevitably marked with an X, previously occupied by a member of the “accelerati incredibilus” family and soon to be a big squish mark containing the bodily remains of the previously mentioned Wile E. Coyote.
Despite having a very limited understanding of it, Gravity is a pretty amazing force, not just for decimating a infinitely resurrecting coyote, but for keeping our feet on the ground and our planet in just the right spot around our Sun. The force due to gravity has got a whole bag of tricks, and reaches across Universal distances. But one of its best tricks is how it acts like a lens, magnifying distant objects for astronomy.
How our horizon might look if Earth orbited the star Artcurus. Credit: TV Roskosmos.
How would our horizon look if Earth orbited around another star, such as Alfa-Centauri, Sirius, or Polaris? Roscosmos TV has released two new videos that replace our familiar Sun and Moon with other stars and planets. While these are completely fantastical — as Earth would have evolved very differently or not evolved at all in orbit around a giant or binary star — the videos are very well done and they give a new appreciation for the accustomed and comforting views we have. The Sun video is above; the Moon below:
Check out Roscosmos TV You Tube page — they have a great collection of videos, from launches to science to fantastical videos like the ones we featured here.
The constellation Orion. Credit: Matthew Spinelli NASA/APOD
Orion dominates the winter sky in the northern hemisphere. Its large size and collection of bright stars — such as Betelgeuse at the shoulder, Rigel below the belt, and the three stars in the belt — make it easy to spot, even for beginning stargazers.
So how about those stars in the belt? They’re one of the most famous asterisms in Western culture, but beyond what we see with our eyes, what are their astronomical properties?
Introduction to Orion
First, a brief word about the constellation itself. In many mythologies, the shape is seen as a human figure — and in Greek mythology, it was named after a hunter, according to a web page from the Chandra X-Ray Observatory.
There are several “reasons” in mythology for why Orion ended up in the sky. One was because he was too boastful about how many animals he could kill — so he was put there to teach humility, since he and his dogs (Canis Major and Canis Minor) chase after animals in the sky but can’t catch them. Some say he died from a scorpion bite, and other legends say he was killed by his lover Artemis accidentally, when her brother Apollo tricked her to shooting an arrow at him.
Wide angle shot of Comet Lovejoy with the constellation Orion, showing rich fields of red nebula, star clouds and dark nebula with the bright green naked eye comet. Credit and copyright: Chris Schur.
Because Orion is on the celestial equator, Chandra adds, it is easy to see all over the world: “Ancient Indians saw the figure as a king who had been shot by an arrow (represented by the stars in Orion’s belt). Ancient Egyptians thought the stars in the belt represented the resting place of the soul of the god Osiris. The Arabs saw the constellation as the figure of a giant.”
The Orion’s belt stars
The three stars in the belt are Mintaka, Alnilam and Alnitak. According to an astronomer with the National Radio Astronomy Observatory, Ronald Maddlaena, these are the meanings of the three stars: Mintaka (on the west) means “belt”, Alnilam (in center) means “belt of pearls” and Altnitak (right) means “girdle.” The three range between 800 and 1,000 light-years from Earth.
The stars “probably formed at about the same time some ten million years ago from the molecular clouds astronomers have found in Orion,” wrote Maddalena.
In this image, the submillimetre-wavelength glow of the dust clouds is overlaid on a view of the region in the more familiar visible light, from the Digitized Sky Survey 2. The large bright cloud in the upper right of the image is the well-known Orion Nebula, also called Messier 42. Credit: ESO/Digitized Sky Survey 2
Here are their properties compared to the Sun:
Mintaka: 20 times more massive and 7,000 times brighter. (Surface temperature 60,000 Fahrenheit.)
Alnilam: 20 times more massive and 18,000 times brigher. (Surface temperature 50,000 Fahrenheit.)
Alnitak: 20 times more massive and 10,000 times brighter. (Surface temperature 60,000 Fahrenheit).
To further blow your mind — these stars also have companion stars orbiting with them, so what you see from Earth with the naked eye isn’t necessarily what you always get.
The European Gaia spacecraft launched about a year ago with the ambitious goal of mapping one billion years in the Milky Way. That’s 1% of all the stars in our entire galaxy, which it will monitor about 70 times over its 5-year mission. If all goes well, we’ll learn an enormous amount about the structure, movements and evolution of the stars in our galaxy. It’ll even find half a million quasars. Continue reading “Astronomy Cast Ep. 365: Gaia”
Before NASA’s Kepler mission searched for exoplanets using the transit method, there was the European COROT mission, launched in 2006. It was sent to search for planets with short orbital periods and find solar oscillations in stars. It was an incredibly productive mission, and the focus of today’s show. Continue reading “Astronomy Cast Ep. 364: The COROT Mission”
The dark nebula LDN 483 imaged by ESO's La Silla Observatory in Chile (ESO)
What may appear at first glance to be an eerie, empty void in an otherwise star-filled scene is really a cloud of cold, dark dust and molecular gas, so dense and opaque that it obscures the distant stars that lie beyond it from our point of view.
Similar to the more well-known Barnard 68, “dark nebula” LDN 483 is seen above in an image taken by the MPG/ESO 2.2-meter telescope’s Wide Field Imager at the La Silla Observatory in Chile.
While it might seem like a cosmic no-man’s-land, no stars were harmed in the making of this image – on the contrary, dark nebulae like LDN 483 are veritable maternity wards for stars. As their cold gas and dust contracts and collapses new stars form inside them, remaining cool until they build up enough density and gravity to ignite fusion within their cores. Then, shining brightly, the young stars will gradually blast away the remaining material with their outpouring wind and radiation to reveal themselves to the galaxy.
The process may take several million years, but that’s just a brief flash in the age of the Universe. Until then, gestating stars within LDN 483 and many other clouds like it remain dim and hidden but keep growing strong.
Wide-field view of the LDN 483 region. (Credit: ESO and Digitized Sky Survey 2)
To a distant observer, our own Milky Way and the Andromeda galaxy would probably look very similar. Although Andromeda is longer, more massive, and more luminous than the Milky Way, both galaxies are vast spirals composed of hundreds of millions of stars. But new research presented at this week’s AAS conference in Seattle suggests that there are other differences as well – namely, in the movement and behavior of certain stellar age groups. This observation is the first of its kind, and raises new questions about the factors that contribute to the formation of spiral galaxies like our own.
Armed with data from both the Hubble Space Telescope and the Keck Observatory in Hawaii, a group of astronomers from UC Santa Cruz resolved 10,000 tiny points of light in the Andromeda galaxy into individual stars and used their spectra to calculate the stars’ ages and velocities – a feat never before accomplished for a galaxy outside of our own.
Led by Puragra Guhathakurta, a professor of astrophysics, and Claire Dorman, a graduate student, the researchers found that in Andromeda, the behavior of older stars is surprisingly more frazzled than that of their younger counterparts; that is, they have a much wider range of velocities around the galactic center. Meanwhile, in the Milky Way, stars of all ages seem to coexist far more peacefully, moving along at the same speed in a consistent, ordered pack.
The astronomers believe that this asymmetry causes Andromeda to look more distinct from our own galaxy than previously thought. “If you could look at [Andromeda’s] disk edge on, the stars in the well-ordered, coherent population would lie in a very thin plane, whereas the stars in the disordered population would form a much puffier layer,” said Dorman.
What could account for such disorderly conduct among Andromeda’s older generation? It is possible that these more mature stars could have been disturbed long ago, during episodes of the kind of “galactic cannibalism” that is thought to go on among most spiral galaxies. Indeed, trails of stars in its outer halo suggest that Andromeda has collided with and consumed a number of smaller galaxies over the course of its lifetime; however, these effects cannot completely account for the jumbled flow of Andromeda’s most elderly stars.
A few examples of galactic cannibalism. NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), K. Noll (STScI), and J. Westphal (Caltech)
Astronomers believe that a second explanation could fill in the blanks – one that owes to events occurring far earlier in history, during the birth of the galaxy itself. After all, if Andromeda originated from a lumpy, irregular gas cloud, its oldest stars would naturally appear fairly disordered. Over time, the parent gas would have settled down, giving rise to ever more organized generations of stars.
Guhathakurta, Dorman, and the rest of the team hope that their work will encourage other scientists to create simulations that will better constrain these possibilities. To them, understanding Andromeda is a vital key to learning more about our own galaxy. Guhathakurta explained, “In the Andromeda galaxy we have the unique combination of a global yet detailed view of a galaxy similar to our own. We have lots of detail in our own Milky Way, but not the global, external perspective.”
Now, thanks to this new research, scientists can cite our own galaxy’s comparative orderliness as strong evidence that we live in a quieter, less cannibalistic neighborhood than most other spiral galaxies in the Universe. “Even the most well ordered Andromeda stars are not as well ordered as the stars in the Milky Way’s disk,” said Dorman.
At least until 4 billion years from now, when the Milky Way and Andromeda collide.
We may as well enjoy the A+ for conduct while we can.
Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold (Credit: Dana Berry, SkyWorks Digital, Inc.)
It’s known as HIP 85605, one of two stars that make up a binary in the Hercules constellation roughly 16 light years away. And if a recent research paper produced by Dr. Coryn Bailer-Jones of the Max Planck Institute for Astronomy in Heidelberg, Germany is correct, it is on a collision course with our Solar System.
Now for the good news: according to Bailer-Jones’ calculations, the star will pass by our Solar System at a distance of 0.04 parsecs, which is equivalent to 8,000 times the distance between the Earth and the Sun (8,000 AUs). In addition, this passage will not affect Earth or any other planet’s orbit around the Sun. And perhaps most importantly of all, none of it will be happening for another 240,000 to 470,000 years from now.
“Even though the galaxy contains very many stars,” Bailer-Jones told Universe Today via email, “the spaces between them are huge. So even over the (long) life of our galaxy so far, the probability of any two stars have actually collided — as opposed to just coming close — is extremely small.”
However, in astronomical terms, that still counts as a near-miss. In a universe that is 46 billion light years in any direction – and that’s just the observable part of it – an event that is expected to take place just 50 light days away is considered to be pretty close. And in the context of space and time, a quarter of a million to half a million years is the very near future.
The real concern is the effect that the passage of HIP 85605 could have on the Oort Cloud – the massive cloud of icy planetesimals that surrounds the Solar System. Given that it’s distance is between 20,000 and 50,000 AU from our Sun, HIP 85605 would actually move through the Oort cloud and cause serious disruption.
The layout of the Solar System, including the Oort Cloud, which lies 50,000 AU from our Sun. Credit: NASA
Many of these planetesimals could be blown off into space, but others could be sent hurtling towards Earth. Assuming humanity is still around at this point in time, this could present a bit of an inconvenience, even if it is spread over the course of a million years.
As it stands, such “close encounters” between stars are quite rare. Stellar collisions usually only occur within binaries, where white dwarfs or neutron stars are concerned. “The exception to this is physically bound binary stars in a tight orbit,” said Bailer-Jones. “It can and does happen that one star expands during its evolution and will then interfere with the evolution of the other star. Neutron-neutron star pairs can even merge.”
But of course, on an astronomical timescale, stars passing each other by as they perform their cosmic dance is actually a pretty common occurrence. As part of Bailer-Jones larger study of over 50,000 stars within our galaxy, this “close encounter” is one of several predicted to take place in the coming years.
Of all of them, only HIP 85605 is expected to come within a single parsec between 240 and 470 thousand years from now. He also indicates with (90% confidence) that the last time such an encounter took place was 3.8 million years ago when gamma Microscopii – a G7 giant which has two and a half times the mass of our Sun – came within 0.35-1.34 pc of our system, which may have caused a large perturbation in the Oort cloud.
Tightly bound binary stars, like the ones illustrated here, sometimes result in stellar collisions. Credit: Chandra
On his MPIA webpage, in the study’s FAQ section, Bailer-Jones claims that his research into stellar close encounters was motivated by a desire to study the potential impacts of astronomical phenomena on Earth, and is part of a larger program named “astroimpacts”.
“I am interested in the history of the Earth,” he says, “and astronomical phenomena have clearly played a role in this. But what role precisely, how significant, and what can we expect to happen in the future?” Whereas several studies have been conducted in the past, he feels that the methods – which include assuming a linear relative motion of stars – produces inaccurate results.”
In contrast, Bailer-Jones study relies on “more recent data or re-analyses of data to produce hopefully more accurate results, and then compensate more rigorously for the uncertainties in the data, so that I can attach probabilities to my statements.”
As a result of this, he predicts that HIP 85605 has a 90% chance of passing within a single parsec of our Sun in the next 240 to 470 thousands years. However, he also admits that if the astronomy is incorrect, the next closest encounter won’t be happening for another 1.3 million years, when a K7 dwarf known as GL 710 is predicted to pass within 0.10 – 0.44 parsecs.
Bailer-Jones also believes that the European Space Agency’s Gaia spacecraft will help make more accurate predictions in the future. By understanding and mapping the environment of the Milky Way Galaxy, measuring the gravitational potential and determining the velocity of stars, scientists will be able to see how their various orbits around the galaxy’s center could cause them to intersect.
It is likely that passing stars have a system of exoplanets (like Kepler-186f pictured here), which would place them within a few parsecs of Earth. Image Credit: NASA Ames/SETI Institute/JPL-CalTech
But perhaps the most interesting question explored on his webpage is the possibility of using stellar close encounters as a shortcut for exploring exoplanets. According to current cosmological models, the majority of stars within our galaxy are believed to host exoplanets.
So if a star is passing us at just a few parsecs (or even with a single parsec) why not hop on over and investigate its planets? Well, as Bailer-Jones indicates, that’s not really a practical idea: “Traveling to a star passing our solar system at a distance of around 1 pc with a relative speed of 30 km/s is no easier than traveling the the nearby stars (the nearest of which is just over 1 pc away). And we would have to wait 10s of thousands of years for the next encounter. If we can ever achieve interstellar travel, I don’t suppose it would take that long to achieve, so why wait?”
Darn. Still, if there’s one thing this phenomena and Bailer-Jones study reminds us, it is that in the course of dancing around the center of the Milky Way, stars are not fixed in a single point in space. Not only do they periodically move within reach of each other, they can also have an affect on life within them.
Alas, the timescale on which such things happen, not to mention the consequences they entail, are so large that people here on Earth need not worry. By the time HIP 85605 or GL 710 come within a parsec or two of us, we’ll either be long-since dead or too highly evolved to care!
*Update: According to a new study posted by Erick E. Mamajek and associates on arXiv, the passage of the recently-discovered low mass star W0720 (aka. “Scholtz Star”) – roughly 70,000 years ago and at a distance of 0.25 Parsecs from our Sun – was the closest encounter our Solar System has had with another star. They calculate the possibility that it would have penetrated the System’s Outer Oort Cloud at 98%. However, they also estimate that the impact it would have had on the flux of long-period comets was negligible, but that the passage also highlights how “dynamically important Oort Cloud perturbers may be lurking among nearby stars”.
Having read the study, Bailer-Jones claims on the updated FAQ section of his MPIA webpage that their analysis appears to be correct. Based on the assumption that the star was moving on a constant velocity relative to the Sun prior to the encounter, he agrees that the calculations on the distances and timing of the passage are valid. While his own study identified a possible closer encounter (Hip 85605), he reiterates that the data on this star is of poor quality. Meanwhile, another close encounter took place involving Hip 89825; but here, the approach distance is estimated to have been 0.02 Parsecs larger. Hence, W0720 can be said to have been the closest encounter with some degree of certainty at this time.
You know the quote, we’re made of stardust. Generation after generation of stars created the materials that make us up. How? And how many stars did it take?
Carl Sagan once said, “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.” To an average person, this might sound completely bananas. I feel it could easily be adopted into the same dirty realm as “My grandpappy wasn’t no gorilla”.
After all, if my teeth are made of stars, and my toothpaste supplier can be believed, why aren’t they brighter and whiter? If my bones are made of stars, shouldn’t I have this creepy inner glow like the aliens from Cocoon? Does this mean everything I eat is made of stars? And conversely, the waste products of my body then are also made of stars? Shouldn’t all this star business include some cool interstellar powers, like Nova? Also, shouldn’t my face be burning?
When the Big Bang happened, 13.8 billion years ago, the entire Universe was briefly the temperature and pressure of a star. And in this stellar furnace, atoms of hydrogen were fused together to make helium and heavier elements like lithium and a little bit of beryllium.
This all happened between 100 and 300 seconds after the Big Bang, and then the Universe wasn’t star-like enough for fusion to happen any more. It’s like someone set a microwave timer and cooked the heck of the whole business for 5 minutes. DING! Your Universe is done! All the other elements in the Universe, including the carbon in our bodies to the gold in our jewelry were manufactured inside of stars.
But how many stars did it take to make “us”? Main sequence stars, like our own Sun, create elements slowly, but surely within their cores. As we speak, the Sun is relentlessly churning hydrogen into helium. Once when it runs out of hydrogen, it’ll switch to crushing helium into carbon and oxygen. More massive stars keep going up the periodic table, making neon and magnesium, oxygen and silicon. But those elements aren’t in you. Once a regular star gets going, it’ll hang onto its elements forever with its intense gravity. Even after it dies and becomes a white dwarf.
White Dwarf Star
No, something needs to happen to get those elements out. That star needs to explode. The most massive stars, ones with dozens of times the mass of our Sun don’t know when to stop. They just keep on churning more and more massive elements, right on up the periodic table. They keep fusing and fusing until they reach iron in their cores. And as iron is the stellar equivalent of ash, fusion reactions no longer generate energy, and instead require energy. Without the fusion energy pushing against the force of gravity pulling everything inward, the massive star collapses in on itself, creating a neutron star or black hole, or detonating as a supernova.
It’s in this moment, a fraction of a second, when all the heavier elements are created. The gold, platinum, uranium and other rare elements that we find on Earth. All of them were created in supernovae in the past. The materials of everything around you was either created during the Big Bang or during a supernova detonation. Only supernovae “explode” and spread their material into the surrounding nebula. Our Solar System formed within a nebula of hydrogen that was enriched by multiple supernovae. Everything around you was pretty much made in a supernova.
These images taken by the Spitzer Space Telescope show the dust and gas concentrations around a supernova. Credit: NASA/JPL-Caltech
So how many? How many times has this cycle been repeated? We don’t know. Lots. There were the original stars that formed shortly after the Big Bang, and then successive generations of massive stars that formed in various nebulae. Astronomers are pretty sure it was a least 3 generations of supernovae, but there’s no way to know exactly.
Carl Sagan said you’re made of star-stuff. But actually you’re made up mostly of Big Bang stuff and generations of supernova stuff. Tasty tasty supernova stuff.
What’s your favorite supernova remnant? Tell us in the comments below.
We hear that rocks are a certain age, and stars are another age. And the Universe itself is 13.7 billion years old. But how do astronomers figure this out?
I know it’s impolite to ask, but, how old are you? And how do you know? And doesn’t comparing your drivers license to your beautiful and informative “Year In Space” calendar feel somewhat arbitrary? How do we know old how everything is when what we observe was around long before calendars, or the Earth, or even the stars?
Scientists have pondered about the age of things since the beginning of science. When did that rock formation appear? When did that dinosaur die? How long has the Earth been around? When did the Moon form? What about the Universe? How long has that party been going on? Can I drink this beer yet, or will I go blind? How long can Spam remain edible past its expiration date?
As with distance, scientists have developed a range of tools to measure the age of stuff in the Universe. From rocks, to stars, to the Universe itself. Just like distance, it works like a ladder, where certain tools work for the youngest objects, and other tools take over for middle aged stuff, and other tools help to date the most ancient.
Let’s start with the things you can actually get your hands on, like plants, rocks, dinosaur bones and meteorites. Scientists use a technique known as radiometric dating. The nuclear age taught us how to blow up stuff real good, but it also helped understand how elements transform from one element to another through radioactive decay.
For example, there’s a version of carbon, called carbon-14. If you started with a kilo of it, after about 5,730 years, half of it would have turned into carbon-12. And then by 5,730 more years, you’d have about ¼ carbon-14 and ¾ carbon-12.
A list of the elements with their corresponding visible light emission spectra. Image Credit: MIT Wavelength Tables, NIST Atomic Spectrum Database, umop.net
This is known as an element’s half-life. And so, if you measure the ratio of carbon-12 to carbon-14 in a dead tree, for example, you can calculate how long ago it lived. Different elements work for different ages. Carbon-14 works for the last 50,000 years or so, while Uranium-238 has a half-life of 4.5 billion years, and will let you date the most ancient of rocks. But what about the stuff we can’t touch, like stars?
When you use a telescope to view a star, you can break up its light into different colors, like a rainbow. This is known as a star’s spectra, and if you look carefully, you can see black lines, or gaps, which correspond to certain elements. Since they can measure the ratios of different elements, astronomers can just look at a star to see how old it is. They can measure the ratio of uranium-238 to lead-206, and know how long that star has been around. How astronomers know the age of the Universe itself is one of my favorites, and we did a whole episode on this.
Artist’s conception of Planck, a space observatory operated by the European Space Agency, and the cosmic microwave background. Credit: ESA and the Planck Collaboration – D. Ducros
The short answer is, they measure the wavelength of the Cosmic Microwave Background Radiation. Since they know this used to be visible light, and has been stretched out by the expansion of the Universe, they can extrapolate back from its current wavelength to what it was at the beginning of the Universe. This tells them the age is about 13.8 billion years. Radiometric dating was a revolution for science. It finally gave us a dependable method to calculate the age of anything and everything, and finally figure out how long everything has been around.
So, fan of our videos. How old are you? Tell us in the comments below.
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