Despite all we know about the formation and evolution of the Universe, the very early days are still kind of mysterious. With our knowledge of physics we can shed some light on the nature of the earliest stars, even though they’re almost certainly long gone.
Now a new discovery is confirming what scientists think they know about the early Universe, by shedding light on a star that’s still shining.
Stars live and die on epic time scales. Tens of millions of years, hundreds of millions of years, even billions of years or longer. Maybe the only thing that surpasses that epicness is when two dead stars join together and come back to life.
In addition to being one of the most beautiful and frequently photographed objects in the night sky, Eta Carinae also has also had the honor of being one of the sky’s most luminous stars for over a century and a half. In addition, it has been a scientific curiosity since its giant ejected nebula (Homunculus) contains information about its parent star.
It is therefore sad news that within a decade or so, we will no longer be able to see the Homunculus nebula clearly. That was the conclusion reached in a new study by an international team of researchers. According to their findings, the nebula will be obscured by the growing brightness of Eta Carinae itself, which will be ten times brighter by about 2036.
The Sun. It’s a big ball of fire, right? Apparently not. In fact, what’s going on inside of the Sun took us some time and knowledge of physics to finally figure out: stellar fusion. Let’s talk about the different kinds of fusion, and how we’re trying to adapt it to generate power here on Earth.
How in the world could you possibly look inside a star? You could break out the scalpels and other tools of the surgical trade, but good luck getting within a few million kilometers of the surface before your skin melts off. The stars of our universe hide their secrets very well, but astronomers can outmatch their cleverness and have found ways to peer into their hearts using, of all things, sound waves. Continue reading “Scientists are Using Artificial Intelligence to See Inside Stars Using Sound Waves”
The Milky Way is an extremely big place. Measured from end to end, our galaxy in an estimated 100,000 to 180,000 light years (31,000 – 55,000 parsecs) in diameter. And it is extremely well-populated, with an estimated 100 to 400 million stars contained within. And according to recent estimates, it is believed that there are as many as 100 billion planets in the Milky Way. And our galaxy is merely one of trillions within the Universe.
So if we were to break it down, just how much matter would we find out there? Estimating how much there is overall would involve some serious math and incredible figures. But what about a single light year? As the most commonly-used unit for measuring the distances between stars and galaxies, determining how much stuff can be found within a single light year (on average) is a good way to get an idea of how stuff is out there.
Even though the name is a little confusing, you probably already know that a light year is the distance that light travels in the space of a year. Given that the speed of light has been measured to 299,792, 458 m/s (1080 million km/h; 671 million mph), the distance light travels in a single year is quite immense. All told, a single light year works out to 9,460,730,472,580.8 kilometers (5,878,625,373,183.6 mi).
So to determine how much stuff is in a light year, we need to take that distance and turn it into a cube, with each side measuring one light year in length. Imagine that giant volume of space (a little challenging for some of us to get our heads around) and imagine just how much “stuff” would be in there. And not just “stuff”, in the sense of dust, gas, stars or planets, either. How much nothing is in there, as in, the empty vacuum of space?
There is an answer, but it all depends on where you put your giant cube. Measure it at the core of the galaxy, and there are stars buzzing around all over the place. Perhaps in the heart of a globular cluster? In a star forming nebula? Or maybe out in the suburbs of the Milky Way? There’s also great voids that exist between galaxies, where there’s almost nothing.
Density of the Milky Way:
There’s no getting around the math in this one. First, let’s figure out an average density for the Milky Way and then go from there. Its about 100,000 to 180,000 light-years across and 1000 light-years thick. According to my buddy and famed astronomer Phil Plait (of Bad Astronomy), the total volume of the Milky Way is about 8 trillion cubic light-years.
And the total mass of the Milky Way is 6 x 1042 kilograms (that’s 6,000 trillion trillion trillion metric tons or 6,610 trillion trillion trillion US tons). Divide those together and you get 8 x 1029 kilograms (800 trillion trillion metric tons or 881.85 trillion trillion US tons) per light year. That’s an 8 followed by 29 zeros. This sounds like a lot, but its actually the equivalent of 0.4 Solar Masses – 40% of the mass of our Sun.
In other words, on average, across the Milky Way, there’s about 40% the mass of the Sun in every cubic light year. But in an average cubic meter, there’s only about 950 attograms, which is almost one femtogram (a quadrillionth of a gram of matter), which is pretty close to nothing. Compare this to air, which has more than a kilogram of mass per cubic meter.
To be fair, in the densest regions of the Milky Way – like inside globular clusters – you can get densities of stars with 100, or even 1000 times greater than our region of the galaxy. Stars can get as close together as the radius of the Solar System. But out in the vast interstellar gulfs between stars, the density drops significantly. There are only a few hundred individual atoms per cubic meter in interstellar space.
And in the intergalactic voids; the gulfs between galaxies, there are just a handful of atoms per meter. Like it or not, much of the Universe is pretty close to being empty space, with just trace amounts of dust or gas particles to be found between all the stars, galaxies, clusters and super clusters.
So how much stuff is there in a light year? It all depends on where you look, but if you spread all the matter around by shaking the Universe up like a snow globe, the answer is very close to nothing.
Dr. Jeffrey Forshaw is a British particle physicist with an interest in quantum chromodynamics (QCD) which is the study of the behavior of subatomic particles. Dr. Forshaw is the co-author (with Brian Cox) of Universal: A Guide to the Cosmos, which sends readers on an inspirational journey of scientific exploration.
We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
The WSH recently welcomed back Mathew Anderson, author of “Our Cosmic Story,” to the show to discuss his recent update. He was kind enough to offer our viewers free electronic copies of his complete book as well as his standalone update. Complete information about how to get your copies will be available on the WSH webpage – just visit http://www.wsh-crew.net/cosmicstory for all the details.
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Gaia is a space observatory parked at the L2 Lagrange Point, a stable place in space a million miles behind Earth as viewed from the Sun. Its mission is astrometry: measuring the precise positions, distances and motion of 1 billion astronomical objects (primarily stars) to create a three-dimensional map of the Milky Way galaxy. Gaia’s radial velocity measurements — the motion of stars toward or away from us — will provide astronomers with a stereoscopic and moving-parts picture of about 1% of the galaxy’s stars.
Think about how slowly stars move from the human perspective. Generations of people have lived and died since the days of ancient Greece and yet the constellations outlines and naked eye stars appear nearly identical today as they did then. Only a few stars — Arcturus, Sirius, Aldebaran — have moved enough for a sharp-eyed observer of yore to perceive their motion.
We know that stars are constantly on the move around the galactic center. The Sun and stars in its vicinity orbit the core at some half-million miles an hour, but nearly all are so far away that their apparent motion has barely moved the needle over the time span of civilization as we know it.
This video shows more than 2 million stars from the TGAS sample, with the addition of 24,320 bright stars from the Hipparcos Catalogue that weren’t included in Gaia’s first data release back in September 2016. The video starts from the positions of stars as measured by Gaia between 2014 and 2015, and shows how these positions are expected to evolve in the future, based on the stars’ proper motions or direction of travel across space.
Watching the show
The frames in the video are separated by 750 years, and the overall sequence covers 5 million years. The dark stripes visible in the early frames reflect the way Gaia scans the sky (in strips) and the early, less complete database. The artifacts are gradually washed out as stars move across the sky.
Using the map above to get oriented, it’s fun to watch Orion change across the millennia. Betelgeuse departs the constellation heading north fairly quickly, but Orion’s Belt hangs in there for nearly 2 million years even if it soon develops sag! The Pleiades drift together to the left and off frame and then reappear at right.
Stars seem to move with a wide range of velocities in the video, with stars in the galactic plane moving quite slow and faster ones speeding across the view. This is a perspective effect: most of the stars we see in the plane are much farther from us, and thus seem to be moving slower than the nearby stars, which are visible across the entire sky.
Some of the stars that appear to zip in and out of view quickly are passing close to the Sun. But motion of those that trace arcs from one side of the sky to the other while passing close to the galactic poles (top and bottom of the frame) as they speed up and slow down, is spurious. These stars move with a constant velocity through space.
Stars located in the Milky Way’s halo, a roughly spherical structure centered on the galaxy’s spiral disk, also appear to move quite fast because they slice through the galactic plane with respect to the Sun. In reality, halo stars move very slowly with respect to the center of the galaxy.
Early in the the visualization, we see clouds of interstellar gas and dust that occupy vast spaces within the galaxy and block the view of more distant suns. That these dark clouds seem to disappear over time is also a spurious effect.
After a few million years, the plane of the Milky Way appears to have shifted towards the right as a consequence of the motion of the Sun with respect to that of nearby stars in the Milky Way. Regions that are depleted of stars in the video will not appear that way to future stargazers but will instead be replenished by stars not currently sampled by Gaia. So yes, there are a few things to keep in mind while watching these positional data converted into stellar motions, but the overall picture is an accurate one.
I find the video as mesmerizing as watching fireflies on a June night. The stars seem alive. Enjoy your ride in the time machine!
It sometimes doesn’t take much to tear a family apart. A Christmas dinner gone wrong can do that. But for a family of stars to be torn apart, something really huge has to happen.
The dramatic break-up of a family of stars played itself out in the Orion Nebula, about 600 years ago. The Orion Nebula is one of the most studied objects in our galaxy. It’s an active star forming region, where much of the star birth is concealed behind clouds of dust. Advances in infrared and radio astronomy have allowed us to peer into the Nebula, and to watch a stellar drama unfolding.
Over the last few decades, observations showed the two of the stars in our young family travelling off in different directions. In fact, they were travelling in opposite directions, and moving at very high speeds. Much higher than stars normally travel at. What caused it?
Astronomers were able to piece the story together by re-tracing the positions of both stars back 540 years. All those centuries ago, around the same time that it was dawning on humanity that Earth revolved around the Sun instead of the other way around, both of the speeding stars were in the same location. This suggested that the two were part of a star system that had broken up for some reason. But their combined energy didn’t add up.
Now, the Hubble has provided another clue to the whole story, by spotting a third runaway star. They traced the third star’s path back 540 years and found that it originated in the same location as the others. That location? An area near the center of the Orion Nebula called the Kleinmann-Low Nebula.
The team behind these new results, led by Kevin Luhman of Penn State University, will release their findings in the March 20, 2017 issue of The Astrophysical Journal Letters.
“The new Hubble observations provide very strong evidence that the three stars were ejected from a multiple-star system,” said Luhman. “Astronomers had previously found a few other examples of fast-moving stars that trace back to multiple-star systems, and therefore were likely ejected. But these three stars are the youngest examples of such ejected stars. They’re probably only a few hundred thousand years old. In fact, based on infrared images, the stars are still young enough to have disks of material leftover from their formation.”
“The Orion Nebula could be surrounded by additional fledging stars that were ejected from it in the past and are now streaming away into space.” – Lead Researcher Kevin Luhman, Penn State University.
The three stars are travelling about 30 times faster than most of the Nebula’s other stellar inhabitants. Theory has predicted the phenomenon of these breakups in regions where newborn stars are crowded together. These gravitational back-and-forths are inevitable. “But we haven’t observed many examples, especially in very young clusters,” Luhman said. “The Orion Nebula could be surrounded by additional fledging stars that were ejected from it in the past and are now streaming away into space.”
The key to this mystery is the recently discovered third star. But this star, the so-called “source x”, was discovered by accident. Luhman is part of a team using the Hubble to hunt for free-floating planets in the Orion Nebula. A comparison of Hubble infrared images from 2015 with images from 1998 showed that source x had changed its position. This indicated that the star was moving at a speed of about 130,000 miles per hour.
Luhmann then re-traced source x’s path and it led to the same position as the other 3 runaway stars 540 years ago: the Kleinmann-Low Nebula.
According to Luhmann, the three stars were most likely ejected from their system due to gravitational fluctuations that should be common in a high-population area of newly-born stars. Two of the stars can come very close together, either forming a tight binary system or even merging. That throws the gravitational parameters of the system out of whack, and other stars can be ejected. The ejection of those stars can also cause fingers of matter to flow out of the system.
As we get more powerful telescopes operating in the infrared, we should be able to clarify exactly what happens in areas of intense star formation like the Orion Nebula and its embedded Kleinmann-Low Nebula. The James Webb Space Telescope should advance our understanding greatly. If that’s the case, then not only will the details of star birth and formation become much clearer, but so will the break up of young families of stars.