milky way Archives

April 30, 2017May 1, 2017 by Bob King

Star-travel 5 Million Years Into The Milky Way’s Future

Two Million Stars on the Move

Gaze into Gaia’s crystal ball and you will see the future. This video shows the motion of 2,057,050 stars in the coming 5 million years from the Tycho-Gaia Astrometric Solution sample, part of the first data release of European Space Agency’s Gaia mission.

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.

Given enough time, stars do change position, distorting the outlines of the their constellations. This view shows the sky looking north in 91,000 A.D. Both Lyra and the Big Dipper are clearly bent out of shape! Created with Stellarium

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.

This frame will help you get your footing as you watch the video. Orion (at right) and the Alpha Persei stellar association and Pleiades (at left) are shown. Credit: ESA/Gaia/DPAC

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.

Artist’s impression of The Milky Way Galaxy to provide context for the video. The Sun and solar system are located in the flat plane of the galaxy, so when we look into the Milky Way (either toward the center or toward the edge), the stars pile up across the light years to form a band in the sky. If we could rise above the disk and see the galaxy from the halo, we’d be able to look down (or up) and see the galaxy as a disk with winding spiral arms. Credit: NASA

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!

March 24, 2017April 4, 2017 by Bob King

Watch Stars Orbit The Milky Way’s Supermassive Black Hole

Stars circle 'round the Milky Way central supermassive black hole. Credit: ESO

The Milky Way’s supermassive black hole, called Sagittarius A* (or Sgr A*), is arrowed in the image made of the innermost galactic center in X-ray light by NASA’s **Chandra Observatory**. To the left or east of Sgr A* is Sgr A East, a large cloud that may be the remnant of a supernova. Centered on Sgr A* is a spiral shaped group of gas streamers that might be falling onto the hole. Credit: NASA/CXC/MIT/Frederick K. Baganoff et al.

When your ordinary citizen learns there’s a supermassive black hole with a mass of 4 million suns sucking on its teeth in the center of the Milky Way galaxy, they might kindly ask exactly how astronomers know this. A perfectly legitimate question. You can tell them that the laws of physics guarantee their existence or that people have been thinking about black holes since 1783. That year, English clergyman John Michell proposed the idea of “dark stars” so massive and gravitationally powerful they could imprison their own light.

This time-lapse movie in infrared light shows how stars in the central light-year of the Milky Way have moved over a period of 14 years. The yellow mark at the image center represents the location of Sgr A*, site of an unseen supermassive black hole.
Credit: A. Eckart (U. Koeln) & R. Genzel (MPE-Garching), SHARP I, NTT, La Silla Obs., ESO

Michell wasn’t making wild assumptions but taking the idea of gravity to a logical conclusion. Of course, he had no way to prove his assertion. But we do. Astronomers now routinely find bot stellar mass black holes — remnants of the collapse of gas-guzzling supergiant stars — and the supermassive variety in the cores of galaxies that result from multiple black hole mergers over grand intervals of time.

Some of the galactic variety contain hundreds of thousands to billions of solar masses, all of it so to speak “flushed down the toilet” and unavailable to fashion new planets and stars. Famed physicist Stephen Hawking has shown that black holes evaporate over time, returning their energy to the knowable universe from whence they came, though no evidence of the process has yet been found.

On September 14, 2013, astronomers caught the largest X-ray flare ever detected from Sgr A*, the supermassive black hole at the center of the Milky Way, using NASA’s Chandra X-ray Observatory. This event was 400 times brighter than the usual X-ray output from the source and was possibly caused when Sgr A*’s strong gravity tore apart an asteroid in its neighborhood, heating the debris to X-ray-emitting temperatures before slurping down the remains.The inset shows the giant flare. Credit: NASA

So how do we really know a massive, dark object broods at the center of our sparkling Milky Way? Astronomers use radio, X-ray and infrared telescopes to peer into its starry heart and see gas clouds and stars whirling about the center at high rates of speed. Based on those speeds they can calculate the mass of what’s doing the pulling.

The Hubble Space Telescope took this photo of the 5000-light-year-long jet of radiation ejected from the active galaxy M87’s supermassive black hole, which is aboutt 1,000 times more massive than the Milky Way’s black hole. Although black holes are dark, matter whirling into their maws at high speed is heated to high temperature, creating a bright disk of material and jets of radiation. Credit: NASA/The Hubble Heritage Team (STScI/AURA)

In the case of the galaxy M87 located 53.5 million light years away in the Virgo Cluster, those speeds tell us that something with a mass of 3.6 billion suns is concentrated in a space smaller than our Solar System. Oh, and it emits no light! Nothing fits the evidence better than a black hole because nothing that massive can exist in so small a space without collapsing in upon itself to form a black hole. It’s just physics, something that Mr. Scott on Star Trek regularly reminded a panicky Captain Kirk.

So it is with the Milky Way, only our black hole amounts to a piddling 4 million-solar-mass light thief confined within a spherical volume of space some 27 million miles in diameter or just shy of Mercury’s perihelion distance from the Sun. This monster hole resides at the location of Sagittarius A* (pronounced A- star), a bright, compact radio source at galactic center about 26,000 light years away.

Video showing a 14-year-long time lapse of stars orbiting Sgr A*

The time-lapse movie, compiled over 14 years, shows the orbits of several dozen stars within the light year of space centered on Sgr A*. We can clearly see the star moving under the influence of a massive unseen body — the putative supermassive black hole. No observations of Sgr A* in visible light are possible because of multiple veils of interstellar dust that lie across our line of sight. They quench its light to the tune of 25 magnitudes.

Merging black holes (the process look oddly biological!). Credit: SXS

How do these things grow so big in the first place? There are a couple of ideas, but astronomers don’t honestly know for sure. Massive gas clouds around early in the galaxy’s history could have collapsed to form multiple supergiants that evolved into black holes which later then coalesced into one big hole. Or collisions among stars in massive, compact star clusters could have built up stellar giants that evolved into black holes. Later, the clusters sank to the center of the galaxy and merged into a single supermassive black hole.

Whichever you chose, merging of smaller holes may explain its origin.

On a clear spring morning before dawn, you can step out to face the constellation Sagittarius low in the southern sky. When you do, you’re also facing in the direction of our galaxy’s supermassive black hole. Although you cannot see it, does it not still exert a certain tug on your imagination?

February 14, 2017February 20, 2017 by Matt Williams

Distance & Speed Of Sun’s Orbit Around Galactic Centre Measured

Artist’s conception of the Gaia telescope backdropped by a photograph of the Milky Way taken at the European Southern Observatory. Credit: ESA/ATG medialab; background: ESO/S. Brunier

In 2013, the European Space Agency deployed the long-awaited Gaia space observatory. As one of a handful of next-generation space observatories that will be going up before the end of the decade, this mission has spent the past few years cataloging over a billion astronomical objects. Using this data, astronomers and astrophysicists hope to create the largest and most precise 3D map of the Milky Way to date.

Though it is almost to the end of its mission, much of its earliest information is still bearing fruit. For example, using the mission’s initial data release, a team of astrophysicists from the University of Toronto managed to calculate the speed at which the Sun orbits the Milky Way. From this, they were able to obtain a precise distance estimate between our Sun and the center of the galaxy for the first time.

For some time, astronomers have been unsure as to exactly how far our Solar System is from the center of our galaxy. Much of this has to do with the fact that it is impossible to view it directly, due to a combination of factors (i.e. perspective, the size of our galaxy, and visibility barriers). As a result, since the year 2000, official estimates have varied between 7.2 and 8.8 kiloparsecs (~23,483 to 28,700 light years).

Astronomy Image Gallery — *Infrared image from Spitzer Space Telescope, showing the stars at the center of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)*

For the sake of their study, the team – which was led by Jason Hunt, a Dunlap Fellow at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto – combined Gaia’s initial release with data from the RAdial Velocity Experiment (RAVE). This survey, which was conducted between 2003 and 2013 by the Australian Astronomical Observatory (AAO), measured the positions, distances, radial velocities and spectra of 500,000 stars.

Over 200,000 of these stars were also observed by Gaia and information on them was included in its initial data release. As they explain in their study, which was published in the Journal of Astrophysical Letters in November 2016, they used this to examined the speeds at which these stars orbit the center of the galaxy (relative to the Sun), and in the process discovered that there was an apparent distribution in their relative velocities.

In short, our Sun moves around the center of the Milky Way at a speed of 240 km/s (149 mi/s), or 864,000 km/h (536,865 mph). Naturally, some of the more than 200,000 candidates were moving faster or slower. But for some, there was no apparent angular momentum, which they attributed to these stars being scattering onto “chaotic, halo-type orbits when they pass through the Galactic nucleus”.

As Hunt explained in Dunlap Institute press release:

“Stars with very close to zero angular momentum would have plunged towards the Galactic center where they would be strongly affected by the extreme gravitational forces present there. This would scatter them into chaotic orbits taking them far above the Galactic plane and away from the Solar neighbourhood… By measuring the velocity with which nearby stars rotate around our Galaxy with respect to the Sun, we can observe a lack of stars with a specific negative relative velocity. And because we know this dip corresponds to 0 km/sec, it tells us, in turn, how fast we are moving.”

*Detection of an unusually bright X-Ray flare from Sagittarius A*, a supermassive black hole in the center of the Milky Way galaxy. Credit: NASA/CXC/Stanford/I. Zhuravleva et al.*

The next step was to combine this information with proper motion calculations of Sagittarius A* – the supermassive black hole believed to be at the center of our galaxy. After correcting for its motion relative to background objects, they were able to effectively triangulate the Earth’s distance from the center of the galaxy. From this, they derived a refined distance of estimate of 7.6 to 8.2 kpc – which works out to about 24,788 to 26,745 light years.

This study builds upon previous work conducted by the study’s co-authors – Prof. Ray Calberg, the current chair of the Department of Astronomy & Astrophysics at the University of Toronto. Years ago, he and Prof. Kimmo Innanen of the Department of Physics and Astronomy at York University conducted a similar study using radial velocity measurement from 400 of the Milky Way’s stars.

But by incorporating data from the Gaia observatory, the UofT team was able to obtain a much more comprehensive data set and narrow the distance to galactic center by a significant amount. And this was based on only the initial data released by the Gaia mission. Looking ahead, Hunt anticipates that further data releases will allow his team and other astronomers to refine their calculations even more.

“Gaia’s final release in late 2017 should enable us to increase the precision of our measurement of the Sun’s velocity to within approximately one km/sec,” he said, “which in turn will significantly increase the accuracy of our measurement of our distance from the Galactic center.”

As more next-generation space telescopes and observatories are deployed, we can expect them to provide us with a wealth of new information about our Universe. And from this, we can expect that astronomers and astrophysicists will begin to shine the light on a number of unresolved cosmological questions.

Further Reading: University of Toronto, The Astrophysical Journal Letters

January 12, 2017January 18, 2017 by Matt Williams

Stars at the Edge of our Galaxy May Have Been Stolen

Artist's impression of The Milky Way Galaxy. Based on current estimates and exoplanet data, it is believed that there could be tens of billions of habitable planets out there. Credit: NASA

Our Milky Way is a pretty vast and highly-populated space. All told, its stars number between 100 and 400 billion, with some estimates saying that it may have as many as 1 trillion. But just where did all these stars come from? Well, as it turns out, in addition to forming many of its own and merging with other galaxies, the Milky Way may have stolen some of its stars from other galaxies.

Such is the argument made by two astronomers from Harvard-Smithsonian Center for Astrophysics. According to their study, which has been accepted for publication in the The Astrophysical Journal, they claim that roughly half of the stars that orbit at the extreme outer edge of the Milky Way were actually stolen from the nearby Sagittarius dwarf galaxy.

At one time, the Sagittarius Dwarf Elliptical Galaxy was thought to be the closest galaxy to our own (a position now held by the Canis Major dwarf galaxy). As one of several dozen dwarf galaxies that surround the Milky Way, it has orbited our galaxy several times in the past. With each passing orbit, it becomes subject to our galaxy’s strong gravity, which has the effect of pulling it apart.

*A model of the tidally shredded Sagittarius dwarf galaxy wrapping around a 3-D representation of the Milky Way disk. Credit: UCLA/D.R. Law*

The long-term effects of this can be seen by looking to the farthest stars in our galaxy, which consist of the eleven stars that are at a distance of about 300,000 light-years from Earth (well beyond the Milky Way’s spiral disk). According the study produced by Marion Dierickx, a graduate student at Harvard University’s Department of Astronomy, half of these stars were taken from the Sagittarius dwarf galaxy in the past.

Professor Avi Loeb, the Frank B. Baird, Jr. Professor of Science at Harvard and Marion Dierickx PhD advisor, co-authored the study – titled, “Predicted Extension of the Sagittarius Stream to the Milky Way Virial Radius“. As he told Universe Today via email:

“We see evidence for streams of stars connected to the core of the galaxy, and indicating that this dwarf galaxy passed multiple times around the Milky Way center and was ripped apart by the tidal gravitational field of the Milky Way. We are all familiar with the tide in the ocean caused by the gravitational pull of the moon, but if the moon was a much more massive object – it would have pulled the oceans apart from the Earth and we would see a stream of vapor stretched away from the Earth.”

For the sake of their study, Dierickx and Loeb ran computer models to simulate the movements of the Sagittarius dwarf over the past 8 billion years. These simulations reproduced the streams of stars stretching away from the Sagittarius dwarf galaxy to the center of our galaxy. They also varied Sagittarius’ velocity and angle of approach to see if the resulting exchanges would match current observations.

Computer-generated image showing the disc of the Milky Way (red oval) and the Sagittarius dwarf galaxy (red dot). The yellow circles represent stars that have been ripped from the Sagittarius dwarf and flung far across space. Credit: Marion Dierickx / CfA

“We attempted to match the distance and velocity data for the core of the Sagitarrius galaxy, and then compared the resulting prediction for the position and velocity of the streams of stars,” said Loeb. “The results were very encouraging for some particular set of initial conditions regarding the start of the Sagittarius galaxy journey when the universe was roughly half its present age.”

What they found was that over time, the Sagittarius dwarf lost about one-third of its stars and nine-tenths of its dark matter to the Milky Way. The end result of this was the creation of three distinct streams of stars that reach one million light-years from galactic center to the very edge of the Milky Way’s halo. Interestingly enough, one of these streams has been predicted by simulations conducted by projects like the Sloan Digital Survey.

The simulations also showed that five of Sagittarius’ stars would end becoming part of the Milky Way. What’s more, the positions and velocities of these stars coincided with five of the most distant stars in our galaxy. The other six do not appear to be from Sagittarius dwarf, and may be the result of gravitational interactions with another dwarf galaxy in the past.

“The dynamics of stars in the extended arms we predict (which is the largest Galactic structure on the sky ever predicted) can be used to measure the mass and structure of the Milky Way,” said Loeb. “The outer envelope of the Milky Way was never probed directly, because no other stream was known to extend that far.”

*Computer model of the Milky Way, the Sagittarius dwarf galaxy, and the looping stream of material between the two. Credit: Tollerud, Purcell and Bullock/UC Irvine*

Given the way the simulations match up with current observations, Dierickx is confident that more Sagittarius dwarf interlopers are out there, just waiting to be found. For instance, future instruments – like the Large Synoptic Survey Telescope (LSST), which is expected to begin full-survey operations by 2022 – may be able to detect the two remaining streams of stars which were predicted by the survey.

Given the time scales and the distances involved, it is rather difficult to probe our galaxy (and by extension, the Universe) to see exactly how it evolved over time. Pairing observational data with computer models, however, has been proven to test our best theories of how things came to be. In the future, thanks to improved instruments and more detailed surveys, we just might know for certain!

And sure to check out this animation of the computer simulation, which shows the effects on the Milky Way’s gravity on the Sagittarius dwarf galaxy’s stars and dark matter.

Further Reading: CfA

January 11, 2017January 11, 2017 by Nancy Atkinson

Confirmed: We Really are ‘Star Stuff’

An artists depiction of how the spectra of elements in the stars of the Milky Way reflect the importance these elements play in human life. Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration.

Scientist Carl Sagan said many times that “we are star stuff,” from the nitrogen in our DNA, the calcium in our teeth, and the iron in our blood.

It is well known that most of the essential elements of life are truly made in the stars. Called the “CHNOPS elements” – carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur – these are the building blocks of all life on Earth. Astronomers have now measured of all of the CHNOPS elements in 150,000 stars across the Milky Way, the first time such a large number of stars have been analyzed for these elements.

“For the first time, we can now study the distribution of elements across our Galaxy,” says Sten Hasselquist of New Mexico State University. “The elements we measure include the atoms that make up 97% of the mass of the human body.”

Astronomers with the Sloan Digital Sky Survey made their observations with the APOGEE (Apache Point Observatory Galactic Evolution Experiment) spectrograph on the 2.5m Sloan Foundation Telescope at Apache Point Observatory in New Mexico. This instrument looks in the near-infrared to reveal signatures of different elements in the atmospheres of stars.

While the observations were used to create a new catalog that is helping astronomers gain a new understanding of the history and structure of our galaxy, the findings also “demonstrates a clear human connection to the skies,” said the team.

While humans are 65% oxygen by mass, oxygen makes up less than 1% of the mass of all of elements in space. Stars are mostly hydrogen, but small amounts of heavier elements such as oxygen can be detected in the spectra of stars. With these new results, APOGEE has found more of these heavier elements in the inner part of the galaxy. Stars in the inner galaxy are also older, so this means more of the elements of life were synthesized earlier in the inner parts of the galaxy than in the outer parts.

So what does that mean for those of us out on the outer edges of one of the Milky Way’s spiral arms, about 25,000 light-years from the center of the galaxy?

“I think it’s hard to say what the specific implications are for when life could arise,” said team member Jon Holtzman, also from New Mexico State, in an email to Universe Today. “We measure typical abundance of CHNOPS elements at different locations, but it’s not so easy to determine at any given location the time history of the CHNOPS abundances, because it’s hard to measure ages of stars. On top of that, we don’t know what the minimum amount of CHNOPS would need to be for life to arise, especially since we don’t really know how that happens in any detail!”

Holtzman added it is likely that, if there is a minimum required abundance, that minimum was probably reached earlier in the inner parts of the Galaxy than where we are.

The team also said that while it’s fun to speculate how the composition of the inner Milky Way Galaxy might impact how life might arise, the SDSS scientists are much better at understanding the formation of stars in our Galaxy.

“These data will be useful to make progress on understanding Galactic evolution,” said team member Jon Bird of Vanderbilt University, “as more and more detailed simulations of the formation of our galaxy are being made, requiring more complex data for comparison.”

Sloan Foundation 2.5m Telescope at Apache Point Observatory. Credit: SDSS.

“It’s a great human interest story that we are now able to map the abundance of all of the major elements found in the human body across hundreds of thousands of stars in our Milky Way,” said Jennifer Johnson of The Ohio State University. “This allows us to place constraints on when and where in our galaxy life had the required elements to evolve, a sort ‘temporal Galactic habitable zone’”.

The catalog is available at the SDSS website, so take a look for yourself at the chemical abundances in our portion of the galaxy.

Source: SDSS

September 12, 2016September 17, 2016 by Bob King

The Big Dipper in the Year 92,000

Stellar motions distort the future sky. Map: Bob King, Source: Stellarium

If we could transport Ptolemy, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged. — If we could transport **Ptolemy**, a famous astronomer who lived circa 90 – 168 A.D. in Alexandria, Egypt, he would have noticed the shift in position of Arcturus, Sirius and Aldebaran since his time. Everything else would appear virtually unchanged.

You go out and look at the stars year after year and never see any of them get up and walk away from their constellations. Take a time machine back to the days of Plato and Socrates and only careful viewing would reveal that just three of the sky’s naked eye stars had budged: Arcturus, Sirius and Aldebaran. And then only a little. Their motion was discovered by Edmund Halley in 1718 when he compared the stars’ positions then to their positions noted by the ancient Greek astronomers. In all three cases, the stars had moved “above a half a degree more Southerly at this time than the Antients reckoned them.”

NGC 4414 is a spiral galaxy that resembles our own Milky Way. I've drawn in the orbits of several stars. Both disk and halo stars orbit about the center but halo stars describe long elliptical orbits. When they plunge through the disk, if they happen to be relatively nearby as is Arcturus, they'll appear to move relatively quickly across the sky. Credit: NASA/ESA — NGC 4414 is a spiral galaxy that resembles our own Milky Way. I’ve drawn in the orbits of several stars. Both disk and halo stars orbit about the center, but halo stars describe long elliptical orbits that take them well beyond the disk. When a star plunges through the disk, if it happens to be relatively nearby as in the case of Arcturus, the star will appear to move relatively quickly across the sky. Both distance and the type of orbit a star has can affect how fast it moves from our perspective. Credit: NASA/ESA with orbits by the author

Stars are incredibly far away. I could throw light years around like I often do here, but the fact is, you can get a real feel for their distance by noting that during your lifetime, none will appear to move individually. The gems of the night and our sun alike revolve around the center of the galaxy. At our solar system’s distance from the center — 26,000 light years or about halfway from center to edge — it takes the sun about 225 million years to make one revolution around the Milky Way.

That’s a LONG time. The other stars we see on a September night take a similar length of time to orbit. Now divide the average lifetime of some 85 years into that number, and you’ll discover that an average star moves something like .00000038% of its orbit around the galactic center every generation. Phew, that ain’t much! No wonder most stars don’t budge in our lifetime.

This graphic, compiled using SkyMap software created by Chris Marriott, shows the motion of Arcturus over — This graphic, made using SkyMap software created by Chris Marriott, shows the motion of Arcturus over a span of 8,000 years.

Sirius, Aldebaran and Arcturus and several other telescopic stars are close enough that their motion across the sky becomes apparent within the span of recorded history. More powerful telescopes, which expand the scale of the sky, can see a great many stars amble within a human lifetime. Sadly, our eyes alone only work at low power!

Precession of Earth's axis maintains it usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. Credit: Wikimedia Commons — Precession of Earth’s axis maintains its usual 23.5 degree tilt, but this causes the axis to describe a circle in the sky like a wobbling top. The photo is an animation that repeats 10 seconds, so hang in there. Credit: Wikimedia Commons

But we needn’t invest billions in building a time machine to zing to the future or past to see how the constellation outlines become distorted by the individual motions of the stars that compose them. We already have one! Just fire up a free sky charting software program like Stellarium and advance the clock. Like most such programs, it defaults to the present, but let’s look ahead. Far ahead.

If we advance 90,000 years into the future, many of the constellations would be unrecognizable. Not only that, but more locally, the precession of Earth’s axis causes the polestar to shift. In 2016, Polaris in the Little Dipper stands at the northernmost point in the sky, but in 90,000 years the brilliant star Vega will occupy the spot. Tugs from the sun and moon on Earth’s equatorial bulge cause its axis to gyrate in a circle over a period of about 26,000 years. Wherever the axis points defines the polestar.

I advanced Stellarium far enough into the future to see how radically the Big Dipper changes shape over time. Notice too that Vega will be the polestar in that distant era. Map: Bob King, Source: Stellarium

Take a look at the Big Dipper. Wow! It’s totally bent out of shape yet still recognizable. The Pointer Stars no longer quite point to Polaris, but with some fudging we might make it work. Vega stands near the pole, and being much closer to us than the rest of Lyra’s stars, has moved considerably farther north, stretching the outline of the constellation as if taffy.

Now let's head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium — Now let’s head backwards in time 92,000 years to 90,000 B.C. The Dipper then was fairly unrecognizable, with both Vega and Arcturus near the pole. Map: Bob King , Source: Stellarium

Time goes on. We look up at the night sky in the present moment, but so much came before us and much will come after. Constellations were unrecognizable in the past and will be again in the future. In a fascinating discussion with Michael Kauper of the Minnesota Astronomical Society at a recent star party, he described the amount of space in and between galaxies as so enormous that “we’re almost not here” in comparison. I would add that time is so vast we’re likewise almost not present. Make the most of the moment.

September 8, 2016October 5, 2016 by Evan Gough

Best Picture Yet Of Milky Way’s Formation 13.5 Billion Years Ago

The Milky Way is like NGC 4594 (pictured), a disc shaped spiral galaxy with around 200 billion stars. The three main features are the central bulge, the disk, and the halo. Credit: ESO

Maybe we take our beloved Milky Way galaxy for granted. As far as humanity is concerned, it’s always been here. But how did it form? What is its history?

Our Milky Way galaxy has three recognized stellar components. They are the central bulge, the disk , and the halo. How these three were formed and how they evolved are prominent, fundamental questions in astronomy. Now, a team of researchers have used the unique property of a certain type of star to help answer these fundamental questions.

The type of star in question is called the blue horizontal-branch star (BHB star), and it produces different colors depending on its age. It’s the only type of star to do that. The researchers, from the University of Notre Dame, used this property of BHB’s to create a detailed chronographic (time) map of the Milky Way’s formation.

This map has confirmed what theories and models have predicted for some time: the Milky Way galaxy formed through mergers and accretions of small haloes of gas and dust. Furthermore, the oldest stars in our galaxy are at the center, and younger stars and galaxies joined the Milky Way over billions of years, drawn in by the galaxy’s growing gravitational pull.

The team who produced this study includes astrophysicist Daniela Carollo, research assistant professor in the Department of Physics at the University of Notre Dame, and Timothy Beers, Notre Dame Chair of Astrophysics. Research assistant professor Vinicius Placco, and other colleagues rounded out the team.

“We haven’t previously known much about the age of the most ancient component of the Milky Way, which is the Halo System,” Carollo said. “But now we have demonstrated conclusively for the first time that ancient stars are in the center of the galaxy and the younger stars are found at longer distances. This is another piece of information that we can use to understand the assembly process of the galaxy, and how galaxies in general formed.”

This dazzling infrared image from NASA's Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. Credit: NASA/JPL-Caltech — This dazzling infrared image from NASA’s Spitzer Space Telescope shows hundreds of thousands of stars crowded into the swirling core of our spiral Milky Way galaxy. Credit: NASA/JPL-Caltech

The Sloan Digital Sky Survey (SDSS) played a key role in these findings. The team used data from the SDSS to identify over 130,000 BHB’s. Since these stars literally “show their age”, mapping them throughout the Milky Way produced a chronographic map which clearly shows the oldest stars near the center of the galaxy, and youngest stars further away.

“The colors, when the stars are at that stage of their evolution, are directly related to the amount of time that star has been alive, so we can estimate the age,” Beers said. “Once you have a map, then you can determine which stars came in first and the ages of those portions of the galaxy. We can now actually visualize how our galaxy was built up and inspect the stellar debris from some of the other small galaxies being destroyed by their interaction with ours during its assembly.”

Astronomers infer, from various data-driven approaches, that different structural parts of the galaxy have different ages. They’ve assigned ages to different parts of the galaxy, like the bulge. That makes sense, since everything can’t be the same age. Not in a galaxy that’s this old. But this map makes it even clearer.

As the authors say in their paper, “What has been missing, until only recently, is the ability to assign ages to individual stellar populations, so that the full chemo-dynamical history of the Milky Way can be assessed.”

This new map, with over 130,000 stars as data points, is a pretty important step in understanding the evolution of the Milky Way. It takes something that was based more on models and theory, however sound they were, and reinforces it with more constrained data.

Update: The chronographic map, as well as a .gif, can be viewed here.

September 7, 2016September 11, 2016 by Bob King

Terzan 5 May Unlock Secret to Milky Way’s Past

Peering through the thick dust clouds of the galactic bulge (center of the galaxy) an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro

Peering through the thick dust clouds of the galactic bulge an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro — Peering through the thick dust clouds of the galactic bulge (center of the galaxy) an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge’s primordial building blocks, most likely the relic of the very early days of the Milky Way. Credit: NASA/ESA/Hubble/F. Ferraro

Not many people have heard of the globular star cluster Terzan 5. It’s a big ball of stars resembling spilled sugar like so many other globular clusters. A very few globulars are bright enough to see with the naked eye; Terzan 5 is faint because it lies far away in the direction of the center of Milky Way galaxy inside its central bulge. Here, the stars that formed at the galaxy’s birth are packed together in great numbers. They are the “old ones” of the Milky Way.

Today, a team of astronomers revealed that Terzan 5 is unlike any globular cluster known. Most Milky Way globulars contain stars of just one age, about 11-12 billion years. They formed around the same time as the Milky Way itself, used up all their available gas early to build stars and then spent the remaining billions of years aging. Most orbit the galaxy’s center in a vast halo like moths whirring around a bright light. Oddball Terzan 5 has two populations aged 12 billion and 4.5 billion years old and it’s located inside the galactic bulge.

Globular clusters are distributed in a spherical halo about the core or bulge in the Milky Way galaxy. The Sun and planets are located well away from the center. From our perspective, most globular clusters appear concentrated in the direction of the galaxy's center. Credit: Science Frontiers Online — Globular clusters are distributed in a spherical halo about the star-rich core or bulge at the center of the disk of the Milky Way galaxy. Credit: Science Frontiers Online

The team used the cameras on the Hubble Space Telescope as well as a host of ground-based telescopes to find compelling evidence for the two distinct kinds of stars. Not only do they show a large gap in age, but the differ in the elements they contain. Terzan 5’s dual populations point to a star formation process that wasn’t continuous but dominated by two distinct bursts of star formation.

“This requires the Terzan 5 ancestor to have large amounts of gas for a second generation of stars and to be quite massive. At least 100 million times the mass of the Sun,” explains Davide Massari, co-author of the study.

Its unusual properties make Terzan 5 the ideal candidate for the title of “living fossil” from the early days of the Milky Way. Current theories on galaxy formation assume that vast clumps of gas and stars interacted to form the primordial bulge of the Milky Way, merging and dissolving in the process.

While the properties of Terzan 5 are uncommon for a globular cluster, they’re very similar to the stars found in the galactic bulge. Remnants of those gaseous clumps appear to have stuck around intact since the days of our galaxy’s birth, one of them evolving into the present day Terzan 5. That makes it a relic from the Milky Way’s infant days and one of the earliest galactic building blocks. Later, the cluster, which held onto some of its remaining gas, experienced a second burst of star formation.

This current model of the Milky Way galaxy shows the yellow-hued galactic bulge formed by ancient stars well along in their evolution, in contrast to the bluer, younger stars in the spiral arms. Credit: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

“Some characteristics of Terzan 5 resemble those detected in the giant clumps we see in star-forming galaxies at high-redshift (galaxies just beginning to form in the remote universe in the far distant past), suggesting that similar assembling processes occurred in the local and in the distant universe at the epoch of galaxy formation,” said Dr. Francesco Ferraro from the University of Bologna, Italy, who headed up the team.

The Milky Way on a late September night offers an opportunity to contemplate the grand form of the galaxy. Credit: Bob King

Terzan 5’s chandelier-like presence is helping astronomers understand how our galaxy was assembled. Reconstructing the past is one of the key occupations of astronomy. The present is continually departing with every passing moment. Soon enough, every piece of information slips into the past tense. In the near-past, which records humanity’s comings and goings, details are often forgotten or lost. The deep past is even worse. With no one around and only scattered clues, astronomers continually look for fragmental remains that when woven into the fabric of a theory, reveal patterns and processes before we came to be.

August 30, 2016September 26, 2016 by Evan Gough

6 Million Years Ago The Milky Way’s Supermassive Black Hole Raged

Artist's concept of Sagittarius A, the supermassive black hole at the center of our galaxy. Credit: NASA/JPL

6 million years ago, when our first human ancestors were doing their thing here on Earth, the black hole at the center of the Milky Way was a ferocious place. Our middle-aged, hibernating black hole only munches lazily on small amounts of hydrogen gas these days. But when the first hominins walked the Earth, Sagittarius A was gobbling up matter and expelling gas at speeds reaching 1,000 km/sec. (2 million mph.)

The evidence for this hyperactive phase in Sagittarius’ life, when it was an Active Galactic Nucleus (AGN), came while astronomers were searching for something else: the Milky Way’s missing mass.

There’s a funny problem in our understanding of our galactic environment. Well, it’s not that funny. It’s actually kind of serious, if you’re serious about understanding the universe. The problem is that we can calculate how much matter we should be able to see in our galaxy, but when we go looking for it, it’s not there. This isn’t just a problems in the Milky Way, it’s a problem in other galaxies, too. The entire universe, in fact.

Our measurements show that the Milky Way has a mass about 1-2 trillion times greater than the Sun. Dark matter, that mysterious and invisible hobgoblin that haunts cosmologists’ nightmares, makes up about five sixths of that mass. Regular, normal matter makes up the last sixth of the galaxy’s mass, about 150-300 billion solar masses. But we can only find about 65 billion solar masses of that normal matter, made up of the familiar protons, neutrons, and electrons. The rest is missing in action.

Astrophysicists at the Harvard-Smithsonian Center for Astrophysics have been looking for that mass, and have written up their results in a new paper.

“We played a cosmic game of hide-and-seek. And we asked ourselves, where could the missing mass be hiding?” says lead author Fabrizio Nicastro, a research associate at the Harvard-Smithsonian Center for Astrophysics (CfA) and astrophysicist at the Italian National Institute of Astrophysics (INAF).

“We analyzed archival X-ray observations from the XMM-Newton spacecraft and found that the missing mass is in the form of a million-degree gaseous fog permeating our galaxy. That fog absorbs X-rays from more distant background sources,” Nicastro continued.

Artist's impression of the ESA's XMM Newton Spacecraft. Image credit: ESA — Artist’s impression of the ESA’s XMM Newton Spacecraft. Image credit: ESA

Nicastro and the other scientists behind the paper analyzed how the x-rays were absorbed and were able to calculate the amount and distribution of normal matter in that fog. The team relied heavily on computer models, and on the XMM-Newton data. But their results did not match up with a uniform distribution of the gaseous fog. Instead, there is an empty “bubble”, where this is no gas. And that bubble extends from the center of the galaxy two-thirds of the way to Earth.

What can explain the bubble? Why would the gaseous fog not be spread more uniformly through the galaxy?

Clearing gas from an area that large would require an enormous amount of energy, and the authors point out that an active black hole would do it. They surmise that Sagittarius A was very active at that time, both feeding on gas falling into itself, and pumping out streams of hot gas at up to 1000 km/sec.

Which brings us to present day, 6 million years later, when the shock-wave caused by that activity has travelled 20,000 light years, creating the bubble around the center of the galaxy.

Another piece of evidence corroborates all this. Near the galactic center is a population of 6 million year old stars, formed from the same material that at one time flowed toward the black hole.

“The different lines of evidence all tie together very well,” says Smithsonian co-author Martin Elvis (CfA). “This active phase lasted for 4 to 8 million years, which is reasonable for a quasar.”

The numbers all match up, too. The gas accounted for in the team’s models and observations add up to 130 billion solar masses. That number wraps everything up pretty nicely, since the missing matter in the galaxy is thought to be between 85 billion and 235 billion solar masses.

This is intriguing stuff, though it’s certainly not the final word on the Milky Way’s missing mass. Two future missions, the European Space Agency’s Athena X-ray Observatory, planned for launch in 2028, and NASA’s proposed X-Ray Surveyor could provide more answers.

Who knows? Maybe not only will we learn more about the missing matter in the Milky Way and other galaxies, we may learn more about the activity at the center of the galaxy, and what ebbs and flows it has gone through, and how that has shaped galactic evolution.

August 24, 2016 by Nancy Atkinson

Experience the Glorious Night Sky Over Yellowstone National Park

A still from the timelapse video 'Hades Exhales,' a timelapse journey through several of Yellowstone National Park's geyser basins. Credit and copyright: Harun Mehmedinovic/Skyglow Productions.

Tomorrow, August 25, 2016, the US National Park Service celebrates its 100th anniversary, and the NPS has been celebrating all year with their “Find Your Park” promotion. But the first national park, Yellowstone National Park, was created 144 years ago. Yellowstone is known for its dramatic canyons, lush forests, and flowing rivers, but might be most famous for its hot springs and gushing geysers.

This new timelapse offers you a chance to “find your dark skies” at Yellowstone, and features the many geysers there, showing the dramatic geothermal features under both day and night skies. But the night skies over these geyser explosions steal the show! It was filmed by Harun Mehmedinovicas part of the Skyglow Project, an ongoing crowdfunded project that explores the effects and dangers of urban light pollution in contrast with some of the most incredible dark sky areas in North America.

SKYGLOWPROJECT.COM : HADES EXHALES from Harun Mehmedinovic on Vimeo.

The Skyglow Project works in collaboration with International Dark-Sky Association, a nonprofit organization fighting to educate the public about light pollution and to preserve the dark skies around the world.

Coming up this weekend, you can enjoy free admission to all 412 national parks from August 25-28, 2016. You can “find your park” and read about special events happening all around the country at FindYourPark.com

A still from the timelapse video 'Hades Exhales,' a timelapse journey through several of Yellowstone National Park's geyser basins. Credit: Harun Mehmedinovic/Skyglow Productions. — A still from the timelapse video ‘Hades Exhales,’ a timelapse journey through several of Yellowstone National Park’s geyser basins. Credit: Harun Mehmedinovic/Skyglow Productions.

Many thanks to Harun Mehmedinovic and Gavin Heffernan of Sunchaser Pictures for continuing their great work with the Skyglow Project and for sharing their incredible videos with Universe Today. Consider supporting their work, as all donations go towards the creation of more videos and images.