An artistic image of the explosion of a star leading to a gamma-ray burst. (Source: FUW/Tentaris/Maciej Fro?ow)
Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.
There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.
Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.
In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.
Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.
In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.
Star trails over Lake Minnewanka in Alberta, Canada. Credit and copyright: Jack-Fusco.
Ready for an adventure? One of our favorite photographers, Jack Fusco, created this stunning travel video for Travel Alberta and viewing it might be enough to make you start packing your bags.
“There’s a certain feeling that you get from standing under a truly dark sky for the first time,” Jack wrote. “Although it’s hard describe the exact feeling of awe that’s felt, it’s an experience that doesn’t leave you. In fact, it’s something that can change you. It can make you forget about sleeping when the sun has set and instead readies you for an adventure. This timelapse is about capturing the adventure of chasing star filled skies and the feeling you get from experiencing it. I hope it inspires people to find their own adventure chasing the stars.”
See some of his beautiful still images from his photo-shoot below:
Chasing Starlight was shot using a Nikon D800E & a Nikon D810 equipped with Nikon 14-24 f/2.8 lenses. See more of Jack’s wonderful work at his website, Instagram, or Jack Fusco Photography.
Aurora over Peyto Lake in Alberta, Canada. Credit and copyright: Jack Fusco.
Viewed from above, we can now see that our gaze takes across the Perseus Arm (toward the constellation Cygnus), parts of the Sagittarius and Scutum-Centaurus arms (toward the constellations Scutum, Sagittarius and Ophiuchus) and across the central bar. Interstellar dust obscures much of the center of the galaxy. Credit: NASA et. all with additions by the author.
The Milky Way Galaxy is an immense and very interesting place. Not only does it measure some 120,000–180,000 light-years in diameter, it is home to planet Earth, the birthplace of humanity. Our Solar System resides roughly 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust particles called the Orion Arm.
But within these facts about the Milky Way lie some additional tidbits of information, all of which are sure to impress and inspire. Here are ten such facts, listed in no particular order:
1. It’s Warped:
For starters, the Milky Way is a disk about 120,000 light years across with a central bulge that has a diameter of 12,000 light years (see the Guide to Space article for more information). The disk is far from perfectly flat though, as can be seen in the picture below. In fact, it is warped in shape, a fact which astronomers attribute to the our galaxy’s two neighbors -the Large and Small Magellanic clouds.
These two dwarf galaxies — which are part of our “Local Group” of galaxies and may be orbiting the Milky Way — are believed to have been pulling on the dark matter in our galaxy like in a game of galactic tug-of-war. The tugging creates a sort of oscillating frequency that pulls on the galaxy’s hydrogen gas, of which the Milky Way has lots of (for more information, check out How the Milky Way got its Warp).
The warp of Spiral Galaxy ESO 510-13 is similar to that of our own. Credit: NASA/Hubble
2. It Has a Halo, but You Can’t Directly See It:
Scientists believe that 90% of our galaxy’s mass consists of dark matter, which gives it a mysterious halo. That means that all of the “luminous matter” – i.e. that which we can see with the naked eye or a telescopes – makes up less than 10% of the mass of the Milky Way. Its halo is not the conventional glowing sort we tend to think of when picturing angels or observing comets.
In this case, the halo is actually invisible, but its existence has been demonstrated by running simulations of how the Milky Way would appear without this invisible mass, and how fast the stars inside our galaxy’s disk orbit the center.
The heavier the galaxy, the faster they should be orbiting. If one were to assume that the galaxy is made up only of matter that we can see, then the rotation rate would be significantly less than what we observe. Hence, the rest of that mass must be made up of an elusive, invisible mass – aka. “dark matter” – or matter that only interacts gravitationally with “normal matter”.
To see some images of the probable distribution and density of dark matter in our galaxy, check out The Via Lactea Project.
3. It has Over 200 Billion Stars:
As galaxies go, the Milky Way is a middleweight. The largest galaxy we know of, which is designated IC 1101, has over 100 trillion stars, and other large galaxies can have as many as a trillion. Dwarf galaxies such as the aforementioned Large Magellanic Cloud have about 10 billion stars. The Milky Way has between 100-400 billion stars; but when you look up into the night sky, the most you can see from any one point on the globe is about 2,500. This number is not fixed, however, because the Milky Way is constantly losing stars through supernovae, and producing new ones all the time (about seven per year).
These images taken by the Spitzer Space Telescope show dust and gas concentrations around a distant supernova. Credit: NASA/JPL-Caltech
4. It’s Really Dusty and Gassy:
Though it may not look like it to the casual observer, the Milky Way is full of dust and gas. This matter makes up a whopping 10-15% of the luminous/visible matter in our galaxy, with the remainder being the stars. Our galaxy is roughly 100,000 light years across, and we can only see about 6,000 light years into the disk in the visible spectrum. Still, when light pollution is not significant, the dusty ring of the Milky Way can be discerned in the night sky.
The thickness of the dust deflects visible light (as is explained here) but infrared light can pass through the dust, which makes infrared telescopes like the Spitzer Space Telescope extremely valuable tools in mapping and studying the galaxy. Spitzer can peer through the dust to give us extraordinarily clear views of what is going on at the heart of the galaxy and in star-forming regions.
5. It was Made From Other Galaxies:
The Milky Way wasn’t always as it is today – a beautiful, warped spiral. It became its current size and shape by eating up other galaxies, and is still doing so today. In fact, the Canis Major Dwarf Galaxy is the closest galaxy to the Milky Way because its stars are currently being added to the Milky Way’s disk. And our galaxy has consumed others in its long history, such as the Sagittarius Dwarf Galaxy.
6. Every Picture You’ve Seen of the Milky Way Isn’t It:
Currently, we can’t take a picture of the Milky Way from above. This is due to the fact that we are inside the galactic disk, about 26,000 light years from the galactic center. It would be like trying to take a picture of your own house from the inside. This means that any of the beautiful pictures you’ve ever seen of a spiral galaxy that is supposedly the Milky Way is either a picture of another spiral galaxy, or the rendering of a talented artist.
Artist’s concept of Sagittarius A, the supermassive black hole at the center of our galaxy. Credit: NASA/JPL-Caltech
Imaging the Milky Way from above is a long, long way off. However, this doesn’t mean that we can’t take breathtaking images of the Milky Way from our vantage point!
7. There is a Black Hole at the Center:
Most larger galaxies have a supermassive black hole (SMBH) at the center, and the Milky Way is no exception. The center of our galaxy is called Sagittarius A*, a massive source of radio waves that is believed to be a black hole that measures 22,5 million kilometers (14 million miles) across – about the size of Mercury’s orbit. But this is just the black hole itself.
All of the mass trying to get into the black hole – called the accretion disk – forms a disk that has 4.6 million times the mass of our Sun and would fit inside the orbit of the Earth. Though like other black holes, Sgr A* tries to consume anything that happens to be nearby, star formation has been detected near this behemoth astronomical phenomenon.
8. It’s Almost as Old as the Universe Itself:
The most recent estimates place the age of the Universe at about 13.7 billion years. Our Milky Way has been around for about 13.6 billion of those years, give or take another 800 million. The oldest stars in our the Milky Way are found in globular clusters, and the age of our galaxy is determined by measuring the age of these stars, and then extrapolating the age of what preceded them.
Though some of the constituents of the Milky Way have been around for a long time, the disk and bulge themselves didn’t form until about 10-12 billion years ago. And that bulge may have formed earlier than the rest of the galaxy.
9. It’s Part of the Virgo Supercluster:
As big as it is, the Milky Way is part of an even larger galactic structures. Our closest neighbors include the Large and Small Magellanic Clouds, and the Andromeda Galaxy – the closest spiral galaxy to the Milky Way. Along with some 50 other galaxies, the Milky Way and its immediate surroundings make up a cluster known as the Local Group.
A mosaic of telescopic images showing the galaxies of the Virgo Supercluster. Credit: NASA/Rogelio Bernal Andreo
And yet, this is still just a small fraction of our stellar neighborhood. Farther out, we find that the Milky Way is part of an even larger grouping of galaxies known as the Virgo Supercluster. Superclusters are groupings of galaxies on very large scales that measure in the hundreds of millions of light years in diameter. In between these superclusters are large stretches of open space where intrepid explorers or space probes would encounter very little in the way of galaxies or matter.
In the case of the Virgo Supercluster, at least 100 galaxy groups and clusters are located within it massive 33 megaparsec (110 million light-year) diameter. And a 2014 study indicates that the Virgo Supercluster is only a lobe of a greater supercluster, Laniakea, which is centered on the Great Attractor.
10. It’s on the move:
The Milky Way, along with everything else in the Universe, is moving through space. The Earth moves around the Sun, the Sun around the Milky Way, and the Milky Way as part of the Local Group, which is moving relative to the Cosmic Microwave Background (CMB) radiation – the radiation left over from the Big Bang.
The CMB is a convenient reference point to use when determining the velocity of things in the universe. Relative to the CMB, the Local Group is calculated to be moving at a speed of about 600 km/s, which works out to about 2.2 million km/h. Such speeds stagger the mind and squash any notions of moving fast within our humble, terrestrial frame of reference!
For many more facts about the Milky Way, visit the Guide to Space, listen to the Astronomy Cast episode on the Milky Way, or visit the Students for the Exploration and Development of Space at seds.org.
Orion (at right), Sirius (bottom) and the pale wintertime Milky Way (center) are well-placed for viewing around 11 o'clock local time in late November. Credit: Bob King
Several nights ago the chill of interstellar space refrigerated the countryside as temperatures fell well below zero. That didn’t discourage the likes of Orion and his seasonal friends Gemini, Perseus and Auriga. They only seemed to grow brighter as the air grew sharper.
Wending between these familiar constellations like a river steaming in the cold was the Milky Way. The name has always been slightly confusing as it refers to both the milky band of starlight and the galaxy itself. Every single star you see at night belongs to our galaxy, a 100,000 light-year-wide flattened disk scintillating with over 400 billion suns.
Face-on (left) and edge-on views of the Milky Way. Our solar system lies in the flat plane of a barred spiral galaxy called the Milky Way. Looking through the plane, the stars pile up to form the Milky Way band. In summer, we face toward the richer, denser core; in winter we look out toward the edge. Credit: NASA with annotations by the author
Earth, Sun and planets huddle together within the mid-plane of the disk, so that when we look straight into it, the density of stars piles up over thousands of light years to form a thick band across the sky. Since most of the stars are very distant and therefore faint, they can’t be seen individually with the naked eye. They blend together to give the Milky Way a milky or hazy look.
During a snowfall, we can see individual flakes nearby but more distant ones increase in number and blend to make a uniform haze similar to what happens when we look across the flat disk of the Milky Way. Credit: Bob King
In a snowstorm, we easily distinguish individual snowflakes falling in front of our face, but looking into the distance, the flakes blend together to create a white, foggy haze. Replace the snowflakes with stars and you have the Milky Way – with a caveat. If we lived in the center of our galaxy, the sky would be milky with stars in all directions just like that snowstorm, but since the Sun occupies the flat plane, they only appear thick when our line of sight is aimed along the galaxy’s equator. Look above and below the disk and the stars quickly thin out as our gaze pierces through the galaxy’s plane and into intergalactic space.
In this view, the ground – Earth – has been removed from the picture and we can see all around us in space. Now we can see that the Milky Way band describes a full circle in the sky. The blue circle represents the galactic equator. The view shows the sky around midnight in early December. The Sun, at lower right, lies in the same direction as the galaxy’s center this month. Source: Stellarium
If you could float in space some distance from the brilliant ball of Earth, you’d see that the Milky Way band passes above, around and below you like a giant hula-hoop. Back on the ground, we can only see about two-thirds of the band over the course of a year. The other third is below the horizon and visible only from the opposite hemisphere, providing yet another good reason to make that trip to Tahiti or Ayers Rock in Australia.
Few know the winter version of the Milky Way that stands above the southeastern horizon around 10:30-11 p.m. local time on moonless nights in early December. No surprise, given it hardly compares to the brightness of the summertime version. This has much to do with where the Sun is located inside the galaxy, some 30,000 light years away from the center or more than halfway to the edge.
Opposite the galaxy’s center lies the anticenter, located near El Nath in the northern horn of Taurus above the constellation Orion. Source: Stellarium
On late fall and winter nights, our planet faces the galaxy’s outer suburbs and countryside where the stars thin out until giving way to relatively starless intergalactic space. Indeed, the anticenter of the Milky Way lies not far from the star El Nath (Beta Tauri) where Taurus meets Auriga. While the hazy band of the Milky Way is still visible through Auriga and Taurus, it’s thin and anemic compared to summer’s billowy star clouds.
The summertime Milky Way from Scorpius to Cygnus is broader and brighter than the winter version because we face toward the galactic center at nightfall. Credit: Stephen Bockhold
At nightfall in July and August, we face toward the galaxy’s center where 30,000 light years worth of stars, star clouds and nebulae stack up to fatten the Milky Way into a bright, chunky arch on summer evenings compared to winter’s thin gruel.
The slanting winter Milky Way touches many of the familiar, bright constellations of December. This map shows the sky facing southeast around 11 o’clock local time in early December or 9 p.m. in late December. Source: Stellarium
The winter Milky Way starts east of brilliant Sirius and grazes the east side of Orion before ascending into Gemini and Auriga and arching over into the western sky to Cassiopeia’s “W”. Binoculars and telescopes resolve it into individual stars and star clusters and help us appreciate what a truly beautiful and rich place our galactic home is.
Few sights that impress us with the scope and scale of where we live than seeing the Milky Way under a dark sky during the silence of a winter night. Picture Earth and yourself as members of that glowing carpet of stars, and when you can’t take the cold anymore, enjoy the delicious pleasure of stepping inside to unwrap and warm up. You’ve been on a long journey.
A still image from the WAVELIGHT timelapse by Gavin Heffernan (SunchaserPictures.com) and Harun Mehmedinovic (Bloodhoney.com).
Created in association with BBC Earth. Used by permission.
Sandstone formations can be amazing, and if you’ve ever seen or heard about the legendary and hard-to-get-to “Wave” formation in Arizona, you’ll agree it would be a stunning location for a night sky photography shoot. Our friend and timelapse guru Gavin Heffernan was commissioned by the BBC to shoot a timelapse video from this location, and it is absolutely stunning.
“As far as I know, this is the first astrophotography timelapse ever filmed at this amazing location,” Gavin told us via email. “We had seen many beautiful night pictures taken there but no actual timelapses, so we went for it!”
Enjoy the video above, as well a some imagery, below:
This is a video where star trails and rock trails collide! It was assembled from over 10,000 stills snagged on two grueling trips. Check out more of Gavin’s work at his Sunchaser Pictures website.
Another still image from the WAVELIGHT timelapse (vimeo.com/112008512) by Gavin Heffernan (SunchaserPictures.com) and Harun Mehmedinovic (Bloodhoney.com). Created in association with BBC Earth. Used by permission.
Our focus on female astronomers continues with Sandra Faber, and Professor of Astronomy at UC Santa Cruz. Faber was part of the team that turned up the Great Attractor, a mysterious mass hidden by the disk of the Milky Way. Continue reading “Astronomy Cast Ep. 358: Modern Women: Sandra Faber”
ESA's Gaia is currently on a five-year mission to map the stars of the Milky Way. Image credit: ESA/ATG medialab; background: ESO/S. Brunier.
Early on the morning of Dec. 19, 2013, the pre-dawn sky above the coastal town of Kourou in French Guiana was briefly sliced by the brilliant exhaust of a Soyuz VS06 rocket as it ferried ESA’s “billion-star surveyor” Gaia into space, on its way to begin a five-year mission to map the precise locations of our galaxy’s stars. From its position in orbit around L2 Gaia will ultimately catalog the positions of over a billion stars… and in the meantime it will also locate a surprising amount of Jupiter-sized exoplanets – an estimated 21,000 by the end of its primary mission in 2019.
And, should Gaia continue observations in extended missions beyond 2019 improvements in detection methods will likely turn up even more exoplanets, anywhere from 50,000 to 90,000 over the course of a ten-year mission. Gaia could very well far surpass NASA’s Kepler spacecraft for exoplanet big game hunting!
“It is not just the number of expected exoplanet discoveries that is impressive”, said former mission project scientist Michael Perryman, lead author on a report titled Astrometric Exoplanet Detection with Gaia. “This particular measurement method will give us planet masses, a complete exoplanet survey around all types of stars in our Galaxy, and will advance our knowledge of the existence of massive planets orbiting far out from their host stars”.
Artist’s impression of a Jupiter-sized exoplanet orbiting an M-dwarf star
The planets Gaia will be able to spot are expected to be anywhere from 1 to fifteen times the mass of Jupiter in orbit around Sun-like stars out to a distance of about 500 parsecs (1,630 light-years) from our own Solar System. Exoplanets orbiting smaller red dwarf stars will also be detectable, but only within about a fifth of that distance.
While other space observatories like NASA’s Kepler and CNES/ESA’s CoRoT were designed to detect exoplanets through the transit method, whereby a star’s brightness is dimmed ever-so-slightly by the silhouette of a passing planet, Gaia will detect particularly high-mass exoplanets by the gravitational wobble they impart to their host stars as they travel around them in orbit. This is known as the astrometric method.
A select few of those exoplanets will also be transiting their host stars as seen from Earth – anywhere from 25 to 50 of them – and so will be observable by Gaia as well as from many ground-based transit-detection observatories.
After some issues with stray light sneaking into its optics, Gaia was finally given the green light to begin science observations at the end of July and has since been diligently scanning the stars from L2, 1.5 million km from Earth.
With the incredible ability to measure the positions of a billion stars each to an accuracy of 24 microarcseconds – that’s like measuring the width of a human hair from 1,000 km – Gaia won’t be “just” an unprecedented galactic mapmaker but also a world-class exoplanet detector! Get more facts about the Gaia mission here.
The team’s findings have been accepted for publication in The Astrophysical Journal.
The Milky Way over Lake Annette in Jasper National Park, Alberta, a Dark Sky Preserve, on October 24, 2014. Credit and copyright: Alan Dyer/Amazing Sky Photography.
Does it get any more gorgeous than this? What an absolutely beautiful view of the night sky over Lake Annette and Whistler’s Mountain in Jasper National Park.
“I shot this at the Lake Annette Star Party, one of the Dark Sky Festival events, using the Canon 60Da and 10-22mm lens at 10mm f/4 and ISO 3200 for 1 minute, untracked,” said prolific astrophotographer Alan Dyer on Flickr. “Shot October 24, 2014, with fresh snow on Whistler across the lake and valley and on a calm night with still waters reflecting the stars.”
Absolutely spell-binding! Click on the image for larger versions on Flickr, and check out more of Alan’s stunning imagery on his website, Amazing Sky Photography.
#MilkyWayMonday
Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
When you look up and see the Milky Way, you’re gazing into the heart of our home galaxy. What, exactly, are we looking at?
Anyone who’s ever been in truly dark skies has seen the Milky Way. The bright band across the sky is unmistakable. It’s a view of our home galaxy from within.
As you stare out into the skies and see that splash of stars, have you ever wondered, what are you looking at? Which parts are towards the inside of the galaxy and which parts are looking out? Where’s that supermassive black hole you’ve heard so much about?
In order to see the Milky Way at all, you need seriously dark skies, away from the light polluted city. As the skies darken, the Milky Way will appear as a hazy fog across the sky.
Imagine it as this vast disk of stars, with the Sun embedded right in it, about 27,000 light-years from the core. We’re seeing the galaxy edge on, from the inside, and so we see the galactic disk as a band that forms a complete circle around the sky.
Which parts you can see depend on your location on Earth and the time of year, but you can always see some part of the disk.
The galactic core of the Milky Way is located in the constellation Sagittarius, which is located to the South of me in Canada, and only really visible during the Summer. In really faint skies, the Milky Way is clearly thicker and brighter in that region.
Want to know the exact point of the galactic core? It’s right… there.
During the Winter, we’re looking away from the galactic core to the outer regions of the galaxy. It still has the same band of stars, but it’s thinner and without the darker clouds of dust that obscure our view to the galactic core.
How do astronomers even know that we’re in a spiral galaxy anyway?
There are two major types of galaxies, spiral galaxies and elliptical galaxies.
Elliptical galaxies are made up of so many galactic collisions, they’re nothing more than vast balls of trillions of stars, with no structure. Because we can see a distinct band in the sky, we know we’re in some kind of spiral.
The differences between elliptical and spiral galaxies is easy to see. M87 at left and M74, both photographed with the Hubble Space Telescope. Credit: NASA/ESA
Astronomers map the arms by looking at the distribution of gas, which pulls together in star forming spiral arms. They can tell how far the major arms are from the Sun and in which direction.
The trick is that half the Milky Way is obscured by gas and dust. So we don’t really know what structures are on the other side of the galactic disk. With more powerful infrared telescopes, we’ll eventually be able to see though the gas and dust and map out all the spiral arms.
If you’ve never seen the Milky Way with your own eyes, you need to. Get far enough away from city lights to truly see the galaxy you live in.
The best resource is “The Dark Sky Finder”, we’ll put a link in the show notes.
Have you ever seen the Milky Way? If not, why not? Let’s hear a story of a time you finally saw it.
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
