Astronomy Archives

December 3, 2014September 19, 2017 by Matt Williams

10 Interesting Facts About the Milky Way

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 Spiral Galaxy ESO 510-13 is warped similar to our own. Credit: NASA/Hubble Heritage Team (STScI / AURA), C. Conselice (U. Wisconsin / STScI/ NASA — *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 the dust and gas concentrations around a supernova. Credit: NASA/JPL-Caltech — *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 — *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!

We have written many interesting articles about the Milky Way for Universe Today. Here’s 10 Interesting Facts about the Milky Way, How Big is the Milky Way?, What is the Closest Galaxy to the Milky Way?, and How Many Stars Are There in the Milky Way?

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.

December 3, 2014December 23, 2015 by David Dickinson

Rise of the Mega Rockets: Comparing Heavy Lift Launch Systems

An Ariane 5 heads spaceward. Credit: Ariane.tv screenshot.

A new generation of space rockets ready to lift new and exciting payloads spaceward is coming to a sky near you.

Tomorrow, a Delta IV Heavy rocket will boost the Orion space capsule on a two orbit journey around the Earth that will test key systems. And though tomorrow’s launch is uncrewed, the Orion Command Module will one day form the core of NASA’s Orion MPCV Multi-Purpose Crew Vehicle and is slated to care out humanity’s first mission to an asteroid and beyond in the next decade.

But a second, lesser known launch also leaves Earth tomorrow as well, atop a rocket that will soon give way to a new generation of lift boosters as launch services vie for new customers. Just over eight hours after the launch of EFT-1, an Ariane 5 rocket lifts off from French Guiana with GSAT-16.

Credit Jason Major. — The EFT-1 Delta IV Heavy posed for roll out. Credit: Jason Major. @JPMajor

Is the ‘battle of the boosters’ heating up?

This comes after the December 2^nd announcement earlier this week by participating members of the European Space Agency to proceed with the development of the next generation Ariane 6 rocket. Also included in the 5.9 billion Euro (7.3 billion USD) budget proposal is funding for the 2018 ExoMars mission, along with further support of ESA’s International Space Station commitments.

To date, ESA has fielded five of its Automated Transfer cargo Vehicles (ATVs) on missions to the International Space Station. ESA will also design the Service Module segment of the Orion MPCV.

“I can summarize this ministerial council by say it was a success… I’d even go so far as to say that it is a great success,” said Jean-Jacques Dordain, the director-general of the European Space Agency.

The Ariane 6 is expected to be on the launch pad by 2020, and will feature two variants capable of placing 5 to 11 tonnes in a geostationary transfer orbit. The solid fuel booster to be incorporated will be based on the Vega rocket design, while the upper stage Vinci engine is already currently in development.

Ariane 6. Credit Wikimedia Commons, SkywalkerPL. — A look at the Ariane 6 rocket. Credit Wikimedia Commons, SkywalkerPL.

The design has been hotly contested among European Space Agency members, many of whom are in favor of other variants based on the upgraded Ariane 5. Some of the largest rockets of all time included those developed by NPO Energia, capable of lofting 100,000 kilograms into low Earth orbit. An Energia N1 Moon rocket exploded on the pad on July 3^rd 1969, effectively ending the Soviet Union’s bid to put a man on the Moon. In comparison, the massive Saturn V rocket — thus far, the largest and most powerful ever fielded by the United States — could deploy the equivalent of 118,000 kg to low Earth orbit and 47,000 kg to a Trans-Lunar Insertion orbit around the Moon.

But that’s just the beginning. Though the Orion capsule will ride atop a United Launch Services Delta IV Heavy tomorrow — a system usually employed for launching clandestine spy satellites — NASA hopes to have its own Space Launch System (SLS) rocket sitting on the pad by the end of 2018. Boeing was awarded the contract for SLS earlier this year, and the system largely rose re-imagined from the ashes of the cancelled Constellation program. The SLS Block 1 is expected to have a lift capacity of 70,000 kg to LEO, while Boeing’s proposed SLS Block 2 variant would, if fielded, have the largest lift capacity of all time at 130,000 kg to LEO. Only the Long March 9 proposed by China approaches that lofty goal.

An artist’s concept of Orion headed towards deep space. Credit: NASA.

And the wild card is Elon Musk’s SpaceX. Already in the game of sending cargo via its Dragon spacecraft to the ISS, SpaceX is developing a reputation for dependability when it comes to getting satellites into orbit at relatively low cost. SpaceX hopes to field its Falcon 9 Heavy with a lift capacity of 53,000 kg to LEO sometime in 2015, and many proposed missions are banking on the the Falcon 9 Heavy as a future service provider for solar system exploration. Certainly, with the recent failure of the Antares rocket on October 28th, SpaceX may look like the more attractive option to many, and the development of the Ariane 6 is expected to face stiff competition in the brave new world of high tech rocketry.

Ever wonder what all of these launch vehicles and spacecraft past and present look like stacked up against each other? There’s a graphic for that, recently featured on Io9:

Credit: Heaney555 — A breakdown and comparison of spacecraft launch systems. Click to enlarge. Credit: Reddit user Heaney555.

From Almaz to Zarya, this is a fascinating study in scale comparison. Be sure to zoom in and check out the tiny ant-like crew compliment of each, also to scale. Of course, the backyard satellite-tracker in us can’t help be notice the brightness-versus size comparison for many of these. For example, the International Space Station on a good pass can appear as bright as Venus at -4^th magnitude — and even look “TIE Fighter shaped” in binoculars — while the smaller Shenzhou and Soyuz modules are often barely visible as they pass overhead. And how we miss watching the Shuttle paired with the International Space Station as they both glided silently by:

But such orbital drama can still be caught if you know when and where to look for it. And speaking of which, viewers in western Australia and the southwestern United States may be able to see Orion and EFT-1 on its first lap around the Earth tomorrow before it fires its engines over the Atlantic headed for a 5,800 km apogee over southern Africa. Assuming EFT-1 lifts off at the beginning of its 159 minute launch window at 7:05 AM EST/12:05 UT, expect it to see it crossing dusk skies over western Australia at 55 minutes after liftoff, and dawn skies for the southwestern U.S. at 95 minutes post-launch respectively.

An awesome sight to behold indeed, marking the start of a brave new era of space exploration.

So what do you, the astute and space-minded reader of Universe Today think? Are the SLS and its kin the lift vehicle(s) of the future, or ‘rockets to nowhere?’ Will they survive the political winds that are bound to blow over the coming decade? Will the Ariane 6 best the Falcon 9 as the lift platform of choice?

One thing is for sure, expect coverage of space exploration drama and more to continue here at Universe Today!

December 3, 2014December 23, 2015 by Bob King

Soar with the Aurora in this Breathtaking Real-time Video

Scene from "Soaring". Credit: Ole Salomonsen

“Soaring” by Ole Salomonsen

We’ve posted many beautiful aurora photos and videos over the years here at Universe Today, but this one about stopped my heart. Titled “Soaring”, it was all shot in real time by Ole Salomonsen, a landscape photographer based in Tromsø, Norway. Salomonsen has been shooting spectacular stills and videos of the northern lights for years. While not the first aurora video done in real time, it’s probably the most successful, high definition effort to date. Ole used a Sony A7S, which he calls “the best low light camera ever”.

It was shot from late August to mid-November in and around the city of Tromsø, as well as on the island of Senja, Norway’s second largest island and a three-hour drive from the city. But what sets this video apart from many is that it shows the aurora unfolding live as if you’re standing right there. No time lapse.

Coronal aurora scene from "Soaring". Credit: Ole Salomonsen — *Coronal aurora scene from “Soaring”. Credit: Ole Salomonsen*

Having witnessed the northern lights many times over the years from my home in northern Minnesota, I can vouch for how close to reality this work truly is. There’s a little more color saturation than what the naked eye would pick up, but the aurora’s changing rhythms are beautifully captured. Ole also mixes in dramatic pan shots taken as if you were running to find a clearing to get the best view. Honestly, that blew me away.

“Although auroras mostly move slowly and majestic, they can also move really fast,” wrote Salomonsen. After seeing the slow undulations of curtains and rays early in the film, you’ll really appreciate the aurora’s other side – its dazzling speed.

“The corona I captured and the lightning fast sequences at the end are some of the most amazing shows I have witnessed in my many years of hunting and filming the lights,” added Ole.

And now for the most amazing part. What you just watched is only a fraction of what Salomonsen has shot during the season. Expect more soon!

December 3, 2014June 25, 2016 by Matt Williams

The Inner Planets of Our Solar System

The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute

Our Solar System is an immense and amazing place. Between its eight planets, 176 moons, 5 dwarf planets (possibly hundreds more), 659,212 known asteroids, and 3,296 known comets, it has wonders to sate the most demanding of curiosities. Our Solar System is made up of different regions, which are delineated based on their distance from the Sun, but also the types of planets and bodies that can be found within them.

In the inner Solar System, we find the “Inner Planets” – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.

For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterparts. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.

The positions and names of planets and dwarf planets in the solar system. Credit: Planets2008/Wikimedia Commons — *The positions and names of planets and dwarf planets in the solar system.*
*Credit: Planets2008/Wikimedia Commons*

This region is also within the “frost line,” which is a little less than 5 AU (about 700 million km) from the Sun. This line represents the boundary in a system where conditions are warm enough that hydrogen compounds such as water, ammonia, and methane are able to take liquid form. Beyond the frost line, these compounds condense into ice grains.Some scientists refer to the frost line as the “Goldilocks Zone” — where conditions for life may be “just right.”

Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.

The terrestrial inner planets are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.

Mercury:

Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. This small planet looks very much like the Earth’s Moon and is even a similar grayish color, and it even has many deep craters and is covered by a thin layer of tiny particle silicates.

Its magnetic field is only about 1 percent that of Earth’s, and it’s very thin atmosphere means that it is hot during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and is comprised mostly of iron and nickel. Mercury is one of the densest planets in the Solar System.

Venus:

Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the Solar System. This atmosphere is composed of 96% carbon dioxide, along with nitrogen and a few other gases. Dense clouds within Venus’ atmosphere are composed of sulphuric acid and other corrosive compounds, with very litter water.

Only two spacecraft have ever penetrated Venus’s thick atmosphere, but it’s not just man-made objects that have trouble getting through. There are fewer crater impacts on Venus than other planets because all but the largest meteors don’t make it through the thick air without disintegrating. Much of Venus’ surface is marked with volcanoes and deep canyons — the biggest of which is over 6400 km (4,000 mi) long.

Venus is often called the “morning star” because, with the exception of Earth’s moon, it’s the brightest object we see in the sky. Like Mercury, Venus has no moon of its own.

Earth:

Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that currently has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight and warmth in, which is also essential for life to survive.

Inner Solar System. Image credit: NASA — *Illustration of the Inner Planets and their orbits around the Sun Image credit: NASA*

Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our Moon, the only one we have, is comprised of a mixture of various rocks and minerals.

Mars:

Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mountain in the Solar System – Olympus Mons – which rises some 21,229 m (69,649 ft) above the surface, and a giant canyon called Valles Marineris. Valles Marineris is 4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi)!

For comparison, the Grand Canyon in Arizona is about 800 km (500 mi) long and 1.6 km (1 mi) deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent (1/5) of the entire distance around Mars. Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well.

A top-down image of the orbits of Earth and Mars. Image: NASA — *A top-down image of the orbits of Earth and Mars. Credit: NASA*

At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one.

Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, but has since evaporated into space. The planet has two small moons called Phobos and Deimos.

Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.

We have written many interesting articles about the inner planets here at Universe Today. Here’s The Solar System Guide as well as The Inner and Outer Planets in Our Solar System.

For more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.

Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.

December 3, 2014November 29, 2019 by Matt Williams

Planets Could Travel Along with Rogue ‘Hypervelocity’ Stars, Spreading Life Throughout the Universe

An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA

Back in 1988, astronomer Jack Hills predicted a type of “rogue”star might exist that is not bound to any particular galaxy. These stars, he reasoned, were periodically ejected from their host galaxy by some sort of mechanism to begin traveling through interstellar space.

Since that time, astronomers have made numerous discoveries that indicate these rogue, traveling stars indeed do exist, and far from being an occasional phenomenon, they are actually quite common. What’s more, some of these stars were found to be traveling at extremely high speeds, leading to the designation of hypervelocity stars (HVS).

And now, in a series of papers that published in arXiv Astrophysics, two Harvard researchers have argued that some of these stars may be traveling close to the speed of light. Known as semi-relativistic hypervelocity stars (SHS), these fast-movers are apparently caused by galactic mergers, where the gravitational effect is so strong that it fling stars out of a galaxy entirely. These stars, the researchers say, may have the potential to spread life throughout the Universe.

This finding comes on the heels of two other major announcements. The first occurred in early November when a paper published in the Astrophysical Journal reported that as many as 200 billion rogue stars have been detected in a cluster of galaxies some 4 billion light years away. These observations were made by the Hubble Space Telescope’s Frontier Fields program, which made ultra-deep multiwavelength observations of the Abell 2744 galaxy cluster.

This was followed by a study published in Science, where an international team of astronomers claimed that as many as half the stars in the entire universe live outside of galaxies.

Using ESO's Very Large Telescope, astronomers have recorded a massive star moving at more than 2.6 million kilometres per hour. Stars are not born with such large velocities. Its position in the sky leads to the suggestion that the star was kicked out from the Large Magellanic Cloud, providing indirect evidence for a massive black hole in the Milky Way's closest neighbour. Credit: ESO — *Image of a moving star captured by the ESO Very Large Telescope, believed to have been ejected from the Large Magellanic Cloud. Credit: ESO*

However, the recent observations made by Abraham Loeb and James Guillochon of Harvard University are arguably the most significant yet concerning these rogue celestial bodies. According to their research papers, these stars may also play a role in spreading life beyond the boundaries of their host galaxies.

In their first paper, the researchers trace these stars to galaxy mergers, which presumably lead to the formation of massive black hole binaries in their centers. According to their calculations, these supermassive black holes (SMBH) will occasionally slingshot stars to semi-relativistic speeds.

“We predict the existence of a new population of stars coasting through the Universe at nearly the speed of light,” Loeb told Universe Today via email. “The stars are ejected by slingshots made of pairs of massive black holes which form during mergers of galaxies.”

These findings have further reinforced that massive compact bodies, widely known as a supermassive black holes (SMBH), exist at the center of galaxies. Here, the fastest known stars exist, orbiting the SMBH and accelerating up to speeds of 10,000 km per second (3 percent the speed of light).

According to Leob and Guillochon, however, those that are ejected as a result of galactic mergers are accelerated to anywhere from one-tenth to one-third the speed of light (roughly 30,000 – 100,000 km per second).

Image of a hypervelocity star found in data from the Sloan Digital Sky Survey. Credit: Vanderbilt University

Observing these semi-relativistic stars could tell us much about the distant cosmos, according to the Harvard researchers. Compared to conventional research, which relied on subatomic particles like photons, neutrinos, and cosmic rays from distant galaxies, studying ejected stars offers numerous advantages.

“Traditionally, cosmologists used light to study the Universe but objects moving less than the speed of light offer new possibilities,” said Loeb. “For example, stars moving at different speeds allow us to probe a distant source galaxy at different look-back times (since they must have been ejected at different times in order to reach us today), in difference from photons that give us just one snapshot of the galaxy.”

In their second paper, the researchers calculate that there are roughly a trillion of these stars out there to be studied. And given that these stars were detected thanks to the Spitzer Space Telescope, it is likely that future generations will be able to study them using more advanced equipment.

All-sky infrared surveys could locate thousands of these stars speeding through the cosmos. And spectrographic analysis could tell us much about the galaxies they came from.

But how could these fast moving stars be capable of spreading life throughout the cosmos?

Could an alien spore really travel light years between different star systems? Well, as long as your theory doesn't require it to still be alive when it arrives - sure it can. — *The Theory of Panspermia argues that life is distributed throughout the universe by celestial objects. Credit: NASA/Jenny Mottar*

“Tightly bound planets can join the stars for the ride,” said Loeb. “The fastest stars traverse billions of light years through the universe, offering a thrilling cosmic journey for extra-terrestrial civilizations. In the past, astronomers considered the possibility of transferring life between planets within the solar system and maybe through our Milky Way galaxy. But this newly predicted population of stars can transport life between galaxies across the entire universe.”

The possibility that traveling stars and planets could have been responsible for the spread of life throughout the universe is likely to have implications as a potential addition to the Theory of Panspermia, which states that life exists throughout the universe and is spread by meteorites, comets, asteroids.

But Loeb told Universe Today that a traveling planetary system could have potential uses for our species someday.

“Our descendants might contemplate boarding a related planetary system once the Milky Way will merge with its sister galaxy, Andromeda, in a few billion years,” he said.

Further Reading: arxiv.org/1411.5022, arxiv.org/1411.5030

December 3, 2014December 23, 2015 by Vanessa Janek

New Cosmological Theory Goes Inflation-Free

This image, the best map ever of the Universe, shows the oldest light in the universe. This glow, left over from the beginning of the cosmos called the cosmic microwave background, shows tiny changes in temperature represented by color. Credit: ESA and the Planck Collaboration.

The Cosmic Microwave Background (CMB) radiation is one of the greatest discoveries of modern cosmology. Astrophysicist George Smoot once likened its existence to “seeing the face of God.” In recent years, however, scientists have begun to question some of the attributes of the CMB. Peculiar patterns have emerged in the images taken by satellites such as WMAP and Planck – and they aren’t going away. Now, in a paper published in the December 1 issue of The Astronomical Journal, one scientist argues that the existence of these patterns may not only imply new physics, but also a revolution in our understanding of the entire Universe.

Let’s recap. Thanks to a blistering ambient temperature, the early Universe was blanketed in a haze for its first 380,000 years of life. During this time, photons relentlessly bombarded the protons and electrons created in the Big Bang, preventing them from combining to form stable atoms. All of this scattering also caused the photons’ energy to manifest as a diffuse glow. The CMB that cosmologists see today is the relic of this glow, now stretched to longer, microwave wavelengths due to the expansion of the Universe.

As any fan of the WMAP and Planck images will tell you, the hallmarks of the CMB are the so-called anisotropies, small regions of overdensity and underdensity that give the picture its characteristic mottled appearance. These hot and cold spots are thought to be the result of tiny quantum fluctuations born at the beginning of the Universe and magnified exponentially during inflation.

Temperature and polarization around hot and cold spots (Credit: NASA / WMAP Science Team)

Given the type of inflation that cosmologists believe occurred in the very early Universe, the distribution of these anisotropies in the CMB should be random, on the order of a Gaussian field. But both WMAP and Planck have confirmed the existence of certain oddities in the fog: a large “cold spot,” strange alignments in polarity known as quadrupoles and octupoles, and, of course, Stephen Hawking’s initials.

In his new paper, Fulvio Melia of the University of Arizona argues that these types of patterns (Dr. Hawking’s signature notwithstanding) reveal a problem with the standard inflationary picture, or so-called ΛCDM cosmology. According to his calculations, inflation should have left a much more random assortment of anisotropies than the one that scientists see in the WMAP and Planck data. In fact, the probability of these particular anomalies lining up the way they do in the CMB images is only about 0.005% for a ΛCDM Universe.

Melia posits that the anomalous patterns in the CMB can be better explained by a new type of cosmology in which no inflation occurred. He calls this model the R(h)=ct Universe, where c is the speed of light, t is the age of the cosmos, and R(h) is the Hubble radius – the distance beyond which light will never reach Earth. (This equation makes intuitive sense: Light, traveling at light speed (c) for 13.7 billion years (t), should travel an equivalent number of light-years. In fact, current estimates of the Hubble radius put its value at about 13.4 billion light-years, which is remarkably close to the more tightly constrained value of the Universe’s age.)

R(h)=ct holds true for both the standard cosmological scenario and Melia’s model, with one crucial difference: in ΛCDM cosmology, this equation only works for the current age of the Universe. That is, at any time in the distant past or future, the Universe would have obeyed a different law. Scientists explain this odd coincidence by positing that the Universe first underwent inflation, then decelerated, and finally accelerated again to its present rate.

Melia hopes that his model, a Universe that requires no inflation, will provide an alternative explanation that does not rely on such fine-tuning. He calculates that, in a R(h)=ct Universe, the probability of seeing the types of strange patterns that have been observed in the CMB by WMAP and Planck is 7–10%, compared with a figure 1000 times lower for the standard model.

So, could this new way of looking at the cosmos be a death knell for ΛCDM? Probably not. Melia himself cites a few less earth-shattering explanations for the anomalous signals in the CMB, including foreground noise, statistical biases, and instrumental errors. Incidentally, the Planck satellite is scheduled to release its latest image of the CMB this week at a conference in Italy. If these new results show the same patterns of polarity that previous observations did, cosmologists will have to look into each possible explanation, including Melia’s theory, more intensively.

December 2, 2014December 23, 2015 by Elizabeth Howell

Famous Hubble Star Explosion Is Expanding, New Animation Reveals

Eta Carinae from Hubble's STIS instrument. Credit: NASA, ESA, and the Hubble SM4 ERO Team

Wow! One of the most famous star explosions captured by the Hubble Space Telescope — several times — shows clear evidence of expansion in this new animation. You can see here the Homunculus Nebula getting bigger and bigger between 1995 and 2008, when Hubble took pictures of the Eta Carinae star system. More details from one of the animation authors below.

“I had the idea to check the Hubble image of Eta Carinae because I know this star rather well,” wrote Philippe Henarejos, one of the authors of the animation, in an e-mail to Universe Today. Henarejos has written several times about the star for the magazine he edits, Ciel et espace (Sky and Space) and also published a French-language book on star histories.

“Telling this story, I realized that astronomers knew for a long time that the Homunculus Nebula was expanding. Also, I knew that the HST had taken many photos of this object since 1995. So I thought that thanks to the very high resolution of the HST images, it could be possible to see the expansion.”

Along with colleague Jean-Luc Dauvergne, Henarejos tracked down two images in the archives and searched for a fixed object that wouldn’t be moving as the expansion occurred, which they decided would be two stars close to the border of the field of view. Then Dauvergne found a third image that clearly showed the expansion happening.

The two gentlemen then verified their findings with astronomer John Martin from the University of Illinois, who maintains a page on Eta Carinae. “He told me that the expansion is real,” Henarejos said.

And the animation is already getting attention. After being published in the new magazine First Light, it was featured today on the Astronomy Picture of the Day website.

Eta Carinae mysteriously brightened about 170 years ago, becoming the second-most luminous object in Earth’s night sky. Then it faded 150 years ago. Astronomers are still examining the system to see what might have caused this.

December 2, 2014December 23, 2015 by Bob King

Observing Challenge: How to See Asteroid Hebe, Mother of Mucho Meteorites

A 3-D model of 6 Hebe based on its light curve. The asteroid is about 120 miles in diameter and orbits in the main asteroid belt between Mars and Jupiter. Credit: Charles University_Josef Durech_Vojtech Sidorin

In the reeds that line the banks of the celestial river Eridanus, you’ll find Hebe on the prowl this month. Discovered in 1847 by German amateur astronomer Karl Ludwig Hencke , the asteroid may hold the key to the origin of the H-chondrites, a large class of metal-rich stony meteorites found in numerous amateur and professional collections around the world. You can now see this interesting minor planet with nothing more than a pair of binoculars or small telescope.

By his looks, I would not deign to tell Karl Henke to give up on anything. — *Judging by his demeanor, it might have been unwise to tell Karl Hencke he was wasting his time looking for asteroids*.

The first four asteroids – Ceres, Pallas, Juno and Vesta – were discovered in quick succession from 1801 to 1807. Then nothing turned up for years. Most astronomers wrongly assumed all the asteroids had been found and moved on to other projects like measuring the orbits of double stars and determining stellar parallaxes. Nothing could have been further from the truth. Hencke, who worked as a postmaster during the day, doggedly persisted in sieving the stars for new asteroids in his free time at night. His systematic search began in 1830. Fifteen years and hundreds of cold nights at the eyepiece later he turned up 5 Astrae (asteroid no. 5) on Dec. 8, 1845, and 6 Hebe on July 1, 1847.

Hebe orbits in the main asteroid belt between Mars and Jupiter with an average distance from the Sun of 225 million miles. It rotates on its axis once every 7.2 hours. Credit: Wikipedia — *Hebe orbits in the main asteroid belt between Mars and Jupiter with an average distance from the Sun of 225 million miles. It spins on its axis once every 7.3 hours. Credit: Wikipedia*

Energized by the finds, astronomers returned to their telescopes with renewed gusto to join in the hunt once again. The rest is history. As of November 2014 there are 415,688 numbered asteroids and a nearly equal number of unnumbered discoveries. Fittingly, asteroid 2005 Hencke honors the man who kept the fire burning.

You'll find Hebe trucking along in Eridanus in December just north of the pair of +3.5 magnitude stars Delta (lleft) and Epsilon Eridani. This map shows stars to magnitude +9.5 and Hebe's position is marked every 5 nights. Source: Chris Marriott's SkyMap software — You’ll find Hebe trucking along in Eridanus this month just north of Delta (left) and Epsilon Eridani, a pair of +3.5 magnitude stars. This map shows stars to magnitude +9.5 with Hebe’s position marked every 5 nights. Click to enlarge. Source: Chris Marriott’s SkyMap software

At 120 miles (190 km) across, Hebe is one of the bigger asteroids (officially 33rd in size in the main belt) and orbits the Sun once every 3.8 years. It will be our guest this final month of the year shining at magnitude +8.2 in early December, +8.5 by mid-month and +8.9 when you don your party hat on New Year’s Eve. All the while, Hebe will loop across the barrens of Eridanus west of Orion. Use the maps here to help track it down. I’ve included a detailed color map above, but also created a “black stars on white” version for those that find reverse charts easier to use.

Use this wide view of the sky to get oriented before honing in with the more detailed map above. Source: Stellarium — Use this wide view of the sky to get oriented before zeroing in with the more detailed map above. Hebe lies just a few degrees north of Delta and Epsilon Eridani for much of December. Best viewing time is from 10 p.m. to 2 a.m. local time early in the month. Source: Stellarium

In more recent times, Hebe’s story takes an interesting turn. Through a study of its gravitational nudges on other asteroids, astronomers discovered that Hebe is a very compact, rocky object, not a loosey-goosey pile of rubble like some asteroids. Its high density provides strong evidence for a composition of both rock and iron. Scientists can determine the approximate composition of an asteroid’s surface by studying its reflectance spectrum, or what colors or wavelengths are reflected back from the object after a portion is absorbed by its surface. They use infrared light because different minerals absorb different wavelengths of infrared light. That data is compared to infrared absorptions from rocks and meteorites found on Earth. Turns out, our friend Hebe’s spectrum is a good match to two classes of meteorites – the H-chondrites, which comprise 40% of known meteorites – and the rarer IIE silicated iron meteorites.

Did this slice of meteorite come from Hebe? I'm holding a small slice of NWA 2710, an H5 chondrite. Credit: Bob King — Did this slice of meteorite come from Hebe? A 12.9-gram specimen of NWA 2710, an H5 stony chondrite, sparkles in the light. The shiny flecks are iron-nickel metal set in a stony matrix. Credit: Bob King

Because Hebe orbits close to an unstable zone in the asteroid belt, any impacts it suffers are soon perturbed by Jupiter’s gravity and launched into trajectories than can include the Earth. When you spot Hebe in your binoculars the next clear night, you might just be seeing where many of the more common space rocks in our collections originated.

December 2, 2014December 23, 2015 by Morgan Rehnberg

Shooting “Color” in the Blackness of Space

A beautiful image of Sasturns tiny moon Daphnis, but where is all the color?

If NASA is so advanced, why are their pictures in black and white?

It’s a question that I’ve heard, in one form or another, for almost as long as I’ve been talking with the public about space. And, to be fair, it’s not a terrible inquiry. After all, the smartphone in my pocket can shoot something like ten high-resolution color images every second. It can automatically stitch them into a panorama, correct their color, and adjust their sharpness. All that for just a few hundred bucks, so why can’t our billion-dollar robots do the same?

The answer, it turns out, brings us to the intersection of science and the laws of nature. Let’s take a peek into what it takes to make a great space image…

Perhaps the one thing that people most underestimate about space exploration is the time it takes to execute a mission. Take Cassini, for example. It arrived at Saturn back in 2004 for a planned four-year mission. The journey to Saturn, however, is about seven years, meaning that the spacecraft launched way back in 1997. And planning for it? Instrument designs were being developed in the mid-1980s! So, when you next see an astonishing image of Titan or the rings here at Universe Today, remember that the camera taking those shots is using technology that’s almost 30 years old. That’s pretty amazing, if you ask me.

But even back in the 1980s, the technology to create color cameras had been developed. Mission designers simply choose not to use it, and they had a couple of great reasons for making that decision.

Perhaps the most practical reason is that color cameras simply don’t collect as much light. Each “pixel” on your smartphone sensor is really made up of four individual detectors: one red, one blue, two green (human eyes are more sensitive to green!). The camera’s software combines the values of those detectors into the final color value for a given pixel. But, what happens when a green photon hits a red detector? Nothing, and therein lies the problem. Color sensors only collect a fraction of the incoming light; the rest is simply lost information. That’s fine here on Earth, where light is more or less spewing everywhere at all times. But, the intensity of light follows one of those pesky inverse-square laws in physics, meaning that doubling your distance from a light source results in it looking only a quarter as bright.

That means that spacecraft orbiting Jupiter, which is about five times farther from the Sun than is the Earth, see only four percent as much light as we do. And Cassini at Saturn sees the Sun as one hundred times fainter than you or I. To make a good, clear image, space cameras need to make use of all the little light available to them, which means making do without those fancy color pixels.

A mosaic of images through different filters on NASA's Solar Dynamics Observatory. Image credit: NASA/SDO/Goddard Space Flight Center — A mosaic of images through different filters on NASA’s Solar Dynamics Observatory. Image credit: NASA/SDO/Goddard Space Flight Center

The darkness of the solar system isn’t the only reason to avoid using a color camera. To the astronomer, light is everything. It’s essentially our only tool for understanding vast tracts of the Universe and so we must treat it carefully and glean from it every possible scrap of information. A red-blue-green color scheme like the one used in most cameras today is a blunt tool, splitting light up into just those three categories. What astronomers want is a scalpel, capable of discerning just how red, green, or blue the light is. But we can’t build a camera that has red, orange, yellow, green, blue, and violet pixels – that would do even worse in low light!

Instead, we use filters to test for light of very particular colors that are of interest scientifically. Some colors are so important that astronomers have given them particular names; H-alpha, for example, is a brilliant hue of red that marks the location of hydrogen throughout the galaxy. By placing an H-alpha filter in front of the camera, we can see exactly where hydrogen is located in the image – useful! With filters, we can really pack in the colors. The Hubble Space Telescope’s Advanced Camera for Surveys, for example, carries with it 38 different filters for a vast array of tasks. But each image taken still looks grayscale, since we only have one bit of color information.

At this point, you’re probably saying to yourself “but, but, I KNOW I have seen color images from Hubble before!” In fact, you’ve probably never seen a grayscale Hubble image, so what’s up? It all comes from what’s called post-processing. Just like a color camera can combine color information from three detectors to make the image look true-to-life, astronomers can take three (or more!) images through different filters and combine them later to make a color picture. There are two main approaches to doing this, known colloquially as “true color” and “false color.”

A "true color" image of the surface of Jupiter's moon Europa as seen by the Galileo spacecraft. Image credit: NASA/JPL-Caltech/SETI Institute — A “true color” image of the surface of Jupiter’s moon Europa as seen by the Galileo spacecraft. Image credit: NASA/JPL-Caltech/SETI Institute

True color images strive to work just like your smartphone camera. The spacecraft captures images through filters which span the visible spectrum, so that, when combined, the result is similar to what you’d see with your own eyes. The recently released Galileo image of Europa is a gorgeous example of this.

Our eyes would never see the Crab Nebula as this Hubble image shows it. Image credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)

False color images aren’t limited by what our human eyes can see. They assign different colors to different features within an image. Take this famous image of the Crab Nebula, for instance. The red in the image traces oxygen atoms that have had electrons stripped away. Blue traces normal oxygen and green indicates sulfur. The result is a gorgeous image, but not one that we could ever hope to see for ourselves.

So, if we can make color images, why don’t we always? Again, the laws of physics step in to spoil the fun. For one, things in space are constantly moving, usually really, really quickly. Perhaps you saw the first color image of comet 67P/Churyumov-Gerasimenko released recently. It’s kind of blurry, isn’t it? That’s because both the Rosetta spacecraft and the comet moved in the time it took to capture the three separate images. When combined, they don’t line up perfectly and the image blurs. Not great!

The first color image of comet 67P/Churyumov-Gerasimenko. Image credit: ESA/Rosetta

But it’s the inverse-square law that is the ultimate challenge here. Radio waves, as a form of light, also rapidly become weaker with distance. When it takes 90 minutes to send back a single HiRISE image from the Mars Reconnaissance Orbiter, every shot counts and spending three on the same target doesn’t always make sense.

Finally, images, even color ones, are only one piece of the space exploration puzzle. Other observations, from measuring the velocity of dust grains to the composition of gases, are no less important to understanding the mysteries of nature. So, next time you see an eye-opening image, don’t mind that it’s in shades of gray. Just imagine everything else that lack of color is letting us learn.

December 1, 2014October 31, 2016 by Matt Williams

What Percent of Earth is Water?

The Earth is often compared to a majestic blue marble, especially by those privileged few who have gazed upon it from orbit. This is due to the prevalence of water on the planet’s surface. While water itself is not blue, water gives off blue light upon reflection.

For those of us confined to living on the surface, the fact that our world is mostly covered in water is a well known fact. But how much of our planet is made up of water, exactly? Like most facts pertaining to our world, the answer is a little more complicated than you might think, and takes into account a number of different qualifications.

Sources of Water:

In simplest terms, water makes up about 71% of the Earth’s surface, while the other 29% consists of continents and islands. To break the numbers down, 96.5% of all the Earth’s water is contained within the oceans as salt water, while the remaining 3.5% is freshwater lakes and frozen water locked up in glaciers and the polar ice caps.

Of that fresh water, almost all of it takes the form of ice: 69% of it, to be exact. If you could melt all that ice, and the Earth’s surface was perfectly smooth, the sea levels would rise to an altitude of 2.7 km.

Illustration showing all of Earth's water, liquid fresh water, and water in lakes and rivers. Credit: Howard Perlman/USGS/Jack Cook/WHOI — *Illustration showing all of Earth’s water, liquid fresh water, and water in lakes and rivers. Credit: Howard Perlman, USGS/illustraion by Jack Cook, WHOI*

Aside from the water that exists in ice form, there is also the staggering amount of water that exists beneath the Earth’s surface. If you were to gather all the Earth’s fresh water together as a single mass (as shown in the image above) it is estimated that it would measure some 1,386 million cubic kilometers (km³) in volume.

Meanwhile, the amount of water that exists as groundwater, rivers, lakes, and streams would constitute just over 10.6 million km³, which works out to a little over 0.7%. Seen in this context, the limited and precious nature of freshwater becomes truly clear.

Volume vs. Mass:

But how much of Earth is water – i.e. how much water contributes to the actual mass of the planet? This includes not just the surface of the Earth, but inside as well. In terms of volume, all of the water on Earth works out to about 1.386 billion cubic kilometers (km³) or 332.5 million cubic miles (mi³) of space.

But in terms of mas, scientists calculate that the oceans on Earth weight about 1.35 x 10¹⁸ metric tonnes (1.488 x 10¹⁸ US tons), which is the equivalent of 1.35 billion trillion kg, or 2976 trillion trillion pounds. This is just 1/4400 the total mass of the Earth, which means that while the oceans cover 71% of the Earth’s surface, they only account for 0.02% of our planet’s total mass.

*Many theories about the origins of water on Earth attribute it to collisions with comets and asteroids. Credit: NASA/JPL/Caltech*

Source of Earth’s Water:

The origin of water on the Earth’s surface, as well as the fact that it has more water than any other rocky planet in the Solar System, are two of long-standing mysteries concerning our planet. Not that long ago, it was believed that our planet formed dry some 4.6 billion years ago, with high-energy impacts creating a molten surface on the infant Earth.

According to this theory, water was brought to the world’s oceans thanks to icy comets, trans-Neptunian objects or water-rich meteoroids (protoplanets) from the outer reaches of the main asteroid belt colliding with the Earth.

However, more recent research conducted by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, has pushed the date of these origins back further. According to this new study, the world’s oceans also date back 4.6 billion years, when all the worlds of the inner Solar System were still forming.

This conclusion was reached by examining meteorites thought to have formed at different times in the history of the Solar System. Carbonaceous chondrite, the oldest meteorites that have been dated to the very earliest days of the Solar System, were found to have the same chemistry as those originating from protoplanets like Vesta. This includes a significance presence of water.

These meteorites are dated to the same epoch in which water was believed to have formed on Earth – some 11 million years after the formation of the Solar System. In short, it now appears that meteorites were depositing water on Earth in its earliest days.

While not ruling out the possibility that some of the water that covers 71 percent of Earth today may have arrived later, these findings suggest that there was enough already here for life to have begun earlier than thought.

We’ve written many articles about the oceans for Universe Today. Here’s How Many Oceans are there in the World?, Earth Has Less Water Than You Think, Where Did Earth’s Water Come From?, Why Doesn’t Earth Have More Water?, Rethinking the Source of Earth’s Water.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth and Episode 363: Where Did Earth’s Water Come From?

Sources: