If you’ve ever looked at Messier 68 through a telescope, you know what a delightful view it is. But the Hubble Space Telescope offers a spectacular, diamond-studded picture of this crowded stellar encampment, a spherical, star-filled region of space known as a globular cluster. This beautiful grouping of stars has been performing a type of stellar dance for perhaps 10 million years.
At a distance of approximately 33,000 light-years, the M68 globular cluster contains at least 2,000 stars that are visible, including 250 giants and 42 variables. It spans 106 light years in diameter.
Mutual gravitational attraction among a cluster’s numerous stars keeps stellar members in check, allowing globular clusters to hang together for many billions of years.
Astronomers can measure the ages of globular clusters by looking at the light of their constituent stars.
The chemical elements leave signatures in this light, and the starlight reveals that stars of globular clusters typically contain fewer heavy elements, such as carbon, oxygen and iron, than stars like the Sun.
Since successive generations of stars gradually create these elements through nuclear fusion, stars having fewer of them are relics of earlier epochs in the Universe.
Indeed, the stars in globular clusters rank among the oldest on record, dating back more than 10 billion years.
More than 150 of these objects surround our Milky Way Galaxy. On a galactic scale, globular clusters are not all that big. In Messier 68’s case, its stars span a volume of space with a diameter of little more than a hundred light-years. The disc of the Milky Way, on the other hand, extends over some 100,000 light-years or more.
Image caption: The globular cluster Messier 68. Credit: ESA/Hubble & NASA
This just in! Astronomers working with the Hubble Space Telescope have spotted a new moon around distant Pluto, bringing the known count up to 5. The image above was released by NASA just minutes ago, showing the Pluto system with its newest member, P5.
This news comes just a couple of weeks shy of the one-year anniversary of the announcement of Pluto’s 4th known moon, still currently named “P4”.
The news was shared this morning by an undoubtedly excited Alan Stern of the Southwest Research Institute (SwRI) on Twitter.
Astronomers estimate P5 to be between 6 and 15 miles (9.6 to 24 km) in diameter. It orbits Pluto in the same plane as the other moons — Charon, Nix, Hydra and P4.
“The moons form a series of neatly nested orbits, a bit like Russian dolls,” said team lead Mark Showalter of the SETI Institute.
A mini-abstract of an upcoming paper lists image sets acquired on 5 separate occasions in June and July. According to the abstract, P5 is 4% as bright as Nix and 50% as bright as P4.
The satellite’s mean magnitude is V = 27.0 +/- 0.3, making it 4 percent as bright as Pluto II (Nix) and half as bright as S/2011 (134340) 1. The diameter depends on the assumed geometric albedo: 10 km if p_v = 0.35, or 25 km if p_v =0.04. The motion is consistent with a body traveling on a near-circular orbit coplanar with the other satellites. The inferred mean motion is 17.8 +/- 0.1 degrees per day (P = 20.2 +/- 0.1 days), and the projected radial distance from Pluto is 42000 +/- 2000 km, placing P5 interior to Pluto II (Nix) and close to the 1:3 mean motion resonance with Pluto I (Charon).
The new detection will help scientists navigate NASA’s New Horizons spacecraft through the Pluto system in 2015, when it makes an historic and long-awaited high-speed flyby of the distant world.
As stars approach the inevitable ends of their lives they run out of stellar fuel and begin to lose a gravitational grip on their outermost layers, which can get periodically blown far out into space in enormous gouts of gas — sometimes irregularly-shaped, sometimes in a neat sphere. The latter is the case with the star above, a red giant called U Cam in the constellation Camelopardalis imaged by the Hubble Space Telescope.
U Cam is an example of a carbon star. This is a rare type of star whose atmosphere contains more carbon than oxygen. Due to its low surface gravity, typically as much as half of the total mass of a carbon star may be lost by way of powerful stellar winds. Located in the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole, U Cam itself is actually much smaller than it appears in Hubble’s picture. In fact, the star would easily fit within a single pixel at the center of the image. Its brightness, however, is enough to saturate the camera’s receptors, making the star look much bigger than it really is.
The shell of gas, which is both much larger and much fainter than its parent star, is visible in intricate detail in Hubble’s portrait. While phenomena that occur at the ends of stars’ lives are often quite irregular and unstable, the shell of gas expelled from U Cam is almost perfectly spherical.
Just in time for summer fireworks season, the Hubble science team has released an image of Herbig-Haro 110, a young star with geysers of hot gas skyrocketing away through interstellar space. Twin jets of heated gas are being ejected in opposite directions from this star that is still in the formation process. The Hubble team says these outflows are fueled by gas falling onto the young star, which is surrounded by a disc of dust and gas. If the disc is the fuel tank, the star is the gravitational engine, and the jets are the exhaust. And even though the plumes of gas look like whiffs of smoke, they are actually billions of times less dense than the smoke from a fireworks display.
More information about this image from the HubbleSite:
Herbig-Haro (HH) objects come in a wide array of shapes, but the basic configuration stays the same. Twin jets of heated gas, ejected in opposite directions away from a forming star, stream through interstellar space. Astronomers suspect that these outflows are fueled by gas accreting onto a young star surrounded by a disk of dust and gas. The disk is the “fuel tank,” the star is the gravitational engine, and the jets are the exhaust.
When these energetic jets slam into colder gas, the collision plays out like a traffic jam on the interstate. Gas within the shock front slows to a crawl, but more gas continues to pile up as the jet keeps slamming into the shock from behind. Temperatures climb sharply, and this curving, flared region starts to glow. These “bow shocks” are so named because they resemble the waves that form at the front of a boat.
In the case of the single HH 110 jet, astronomers observe a spectacular and unusual permutation on this basic model. Careful study has repeatedly failed to find the source star driving HH 110, and there may be good reason for this: perhaps the HH 110 outflow is itself generated by another jet.
Astronomers now believe that the nearby HH 270 jet grazes an immovable obstacle — a much denser, colder cloud core — and gets diverted off at about a 60-degree angle. The jet goes dark and then reemerges, having reinvented itself as HH 110.
The jet shows that these energetic flows are like the erratic outbursts from a Roman candle. As fast-moving blobs of gas catch up and collide with slower blobs, new shocks arise along the jet’s interior. The light emitted from excited gas in these hot blue ridges marks the boundaries of these interior collisions. By measuring the current velocity and positions of different blobs and hot ridges along the chain within the jet, astronomers can effectively “rewind” the outflow, extrapolating the blobs back to the moment when they were emitted. This technique can be used to gain insight into the source star’s history of mass accretion.
This image is a composite of data taken with Hubble’s Advanced Camera for Surveys in 2004 and 2005 and the Wide Field Camera 3 in April 2011.
Since its discovery in 2005, exoplanet HD 189733b has been one of the most-observed extra solar planets, due to its size, compact orbit, proximity to Earth and enticing blue-sky atmosphere. But astronomers using the Hubble Space Telescope and the Swift Telescope have witnessed dramatic changes in the planet’s upper atmosphere following a violent flare from its parent which bathed the planet in intense X-ray radiation. The scientists say being able to watch the action gives a tantalizing glimpse of the changing climates and weather on planets outside our Solar System.
While HD 189733b has a blue sky like Earth, it is one of the many “hot Jupiters” that have been the easiest for exoplanet hunters to find: huge gas planets that orbit extremely close to its star. HD 189733 lies extremely close to its star, called HD 189733A, just one thirtieth the distance Earth is from the Sun, whipping around the star in 2.2 days. Additionally, the system is just 63 light-years away, so close that its star can be seen with binoculars near the famous Dumbbell Nebula.
Even though its star is slightly smaller and cooler than the Sun, this makes the planet’s climate exceptionally hot, at above 1000 degrees Celsius, and the upper atmosphere is battered by energetic extreme-ultraviolet and X-ray radiation.
Even though HD 189733b’s atmosphere wasn’t thought to be evaporating (like a similar exoplanet called Osiris, or HD 209458b) astronomers knew the potential was there. The atmospheric gases extend far beyond the planetary “surface” allowing stellar light to pass through, and in previous observations astronomers were able to get a peek into what chemical compounds surround HD 189733b. From this analysis, scientists deduced that water and methane is contained in the atmosphere; and later, the Spitzer space telescope even mapped the temperature distribution around the globe. Additional research indicated a thin layer of particles exists in the upper atmosphere of HD 189733b, creating thin reflective clouds.
Astronomer Alain Lecavelier des Etangs from at the Paris Institute of Astrophysics in France led a team using Hubble to observe the atmosphere of this planet during two periods in early 2010 and late 2011, as it was silhouetted against its parent star. While backlit in this way, the planet’s atmosphere imprints its chemical signature on the starlight, allowing astronomers to decode what is happening on scales that are too tiny to image directly. They were hoping to observe the atmosphere evaporating away, but were disappointed in 2010.
“The first set of observations were actually disappointing,” Lecavelier said, “since they showed no trace of the planet’s atmosphere at all. We only realized we had chanced upon something more interesting when the second set of observations came in.”
The team’s follow-up observations, made in 2011, showed a dramatic change, with clear signs of a plume of gas being blown from the planet at a rate of at least 1000 tons per second, at speeds of 300,000 mph, giving the planet a comet-like appearance.
“We hadn’t just confirmed that some planets’ atmospheres evaporate,” Lecavelier said, “we had watched the physical conditions in the evaporating atmosphere vary over time. Nobody had done that before.”
So why was the atmosphere’s condition changing?
Despite the extreme temperature of the planet, the atmosphere is not hot enough to evaporate at the rate seen in 2011. Instead the evaporation is thought to be driven by the intense X-ray and extreme-ultraviolet radiation from the parent star, which is about 20 times more powerful than that of our own Sun. Taking into account also that HD 189733b is a giant planet very close to its star, then it must suffer an X-ray dose 3 million times higher than the Earth.
Because X-rays and extreme ultraviolet starlight heat the planet’s atmosphere and likely drive its escape, the team also monitored the star with Swift’s X-ray Telescope (XRT). On Sept. 7, 2011, just eight hours before Hubble was scheduled to observe the transit, Swift was monitoring the star when it unleashed a powerful flare. It brightened by 3.6 times in X-rays, a spike occurring atop emission levels that already were greater than the sun’s.
“The planet’s close proximity to the star means it was struck by a blast of X-rays tens of thousands of times stronger than the Earth suffers even during an X-class solar flare, the strongest category,” said co-author Peter Wheatley, a physicist at the University of Warwick in England.
After accounting for the planet’s enormous size, the team notes that HD 189733b encountered about 3 million times as many X-rays as Earth receives from a solar flare at the threshold of the X class.
“X-ray emissions are a small part of the star’s total output, but it is the part that it is energetic enough to drive the evaporation of the atmosphere,” said co-author Peter Wheatley from the University of Warwick, in the UK. “This was the brightest X-ray flare from HD 189733A of several observed to date, and it seems very likely that the impact of this flare on the planet drove the evaporation seen a few hours later with Hubble.”
The team also said the changes in the star’s output may mean it undergoes a seasonal process similar to the Sun’s 11-year sunspot cycle.
The team hopes to clarify the changes they witnessed using future observations with Hubble and ESA’s XMM-Newton X-ray space telescope, but say there is no question that the planet was hit by a stellar flare, and no question that the rate of evaporation of the planet’s atmosphere shot up.
This research shows the benefits of collaborative research between missions, as Swift saw the flare, and Hubble saw the massive amount of gas stripped out of the planet’s atmosphere. It also gives potential for future research, to watch for changes in both the star and atmospheres of other worlds.
This video from NASA’s Goddard Spaceflight Center provides additional information:
Lead image caption: This artist’s rendering illustrates the evaporation of HD 189733b’s atmosphere in response to a powerful eruption from its host star. NASA’s Hubble Space Telescope detected the escaping gases and NASA’s Swift satellite caught the stellar flare. Credit: NASA’s Goddard Space Flight Center.
Second image caption: Swift’s Ultraviolet/Optical Telescope captured this view of HD 189733b’s star on Sept. 14, 2011. The image is 6 arcminutes across. Credit: NASA/Swift/Stefan Immler
The image above looks like a classic example of a collision between two galaxies. However, Hubble scientists have determined, this is just an illusion, a trick of perspective. The two galaxies, NGC 3314A and B are actually tens of millions of light years apart instead of merging in a galactic pileup. From our vantage point on Earth the two just happen to appear to be overlapping at great distances from each other.
How did the Hubble scientists figure this out? The biggest hint as to whether galaxies are interacting is usually their shapes. The immense gravitational forces involved in galactic mergers are enough to pull a galaxy out of shape long before it actually collides. Deforming a galaxy like this does not just warp its structure, but it can trigger new episodes of star formation, usually visible as bright blue stars and glowing nebulae.
In the case of NGC 3314, there is some deformation in the foreground galaxy (called NGC 3314A, NGC 3314B lies in the background), but the Hubble team says this is almost certainly misleading. NGC 3314A’s deformed shape, particularly visible below and to the right of the core, where streams of hot blue-white stars extend out from the spiral arms, is not due to interaction with the galaxy in the background.
Studies of the motion of the two galaxies indicate that they are both relatively undisturbed, and that they are moving independently of each other. This indicates in turn that they are not, and indeed have never been, on any collision course. NGC 3314A’s warped shape is likely due instead to an encounter with another galaxy, perhaps nearby NGC 3312 (visible to the north in wide-field images) or another nearby galaxy.
The chance alignment of the two galaxies is more than just a curiosity, though. It greatly affects the way the two galaxies appear to us.
NGC 3314B’s dust lanes, for example, appear far lighter than those of NGC 3314A. This is not because that galaxy lacks dust, but rather because they are lightened by the bright fog of stars in the foreground. NGC 3314A’s dust, in contrast, is backlit by the stars of NGC 3314B, silhouetting them against the bright background.
Such an alignment of galaxies is also helpful to astronomers studying gravitational microlensing, a phenomenon that occurs when stars in one galaxy cause small perturbations in the light coming from a more distant one. Indeed, the observations of NGC 3314 that led to this image were carried out in order to investigate this phenomenon.
This mosaic image covers a large field of view (several times the size of an individual exposure from Hubble’s Advanced Camera for Surveys). Thanks to a long exposure time of more than an hour in total exposure time for every frame, the image shows not only NGC 3314, but also many other more distant galaxies in the background.
The color composite was produced from exposures taken in blue and red light.
Image caption: The Hubble Space Telescope has produced an incredibly detailed image of a pair of overlapping galaxies called NGC 3314. While the two galaxies look as if they are in the midst of a collision, this is in fact a trick of perspective: the two are in chance alignment from our vantage point. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and W. Keel (University of Alabama)
The transit of the Hubble Space Telescope across the Sun was taken from Queensland, Australia, simultaneously with the 2012 transit of Venus. Credit: Thierry Legault.
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Astrophotographer Thierry Legault had told us he was traveling to Australia for the Transit of Venus, so we knew he had something special planned. But that still didn’t prepare us for the awesomeness of what he has just achieved. During the Transit of Venus, Legault also captured the Hubble Space Telescope moving across the face of the Sun. Not once, but 9 times, during the HST’s transit time of .97 seconds. “Thanks to the continuous shooting mode of the Nikon D4 DSLR running at 10 fps,” Legault said on his website, which shows his new images. Of course, due to the differences in distance from Earth of Hubble vs. Venus, Venus took a lazy 6-plus hours to make its transit. A few giant sunspots also join in the view.
Below see a close-up of the two transits and a look at Legault’s set-up in the Outback of Queensland.
A close-up of Venus and Hubble (tiny black dots just above Venus) transiting the Sun. Credit: Thierry Legault. Used by permission.Legault's equipment setup for viewing the Venus Transit in Queensland, Australia. Credit: Thierry Legault. Used by permission.
Legault noted that just one of the telescope/camera setups was his. So, he had just one chance of capturing the double transit. And he nailed it.
Here’s the map from CalSky of where the HST transit would be visible, just a thin band across the top of Queensland:
Map from CalSky of the Hubble Transit. Via Thierry Legault.
Legault said he has some more images on the way, including the ring of the atmosphere of Venus around the first contact, images of the transit in H-alpha, and the full ring of Venus 24 hours after the transit, so keep checking his website for more fantastic images.
Congratulations to Thierry Legault for a truly amazing and special capture of the Transit of Venus, something that won’t happen again in our lifetimes. And thanks to Thierry for sharing his images with Universe Today.
Could two unused satellites given to NASA help resurrect the proposed WFIRST mission? Credit: NASA
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NASA will be getting two unused space surveillance satellites from the US’s National Reconnaissance Office, which could possibly be used to search for dark energy. In articles in the Washington Post and the New York Times, NASA and NRO officials revealed the two unused and not-fully-built satellites are available for NASA to use as they see fit. While the satellites don’t have astronomical instruments and are still in a warehouse, they do have 2.4-meter (7.9 feet) mirrors, just like Hubble, with a wider field of view and a maneuverable secondary mirror that makes it possible to obtain better-focused images.
“This is a total game changer,” said David N. Spergel of Princeton, quoted in the New York Times, who is co-chairman of a committee on astronomy and astrophysics for the National Academy of Sciences.
Reportedly, the NRO contacted NASA in 2011 about the two spy satellites. Since taking over as head of the NASA Science Directorate early this year, former Hubble repairman John Grunsfeld has been working with scientists and other NASA officials to quietly study the possibility of using the two satellites as “repurposed telescopes.”
Originally designed to look at Earth for surveillance, the two telescopes could be turned to look at the heavens instead, as the National Reconnaissance Office said they no longer needed them for spy missions. Why two such spy telescopes were under construction and then scrapped is not clear.
Described as not fully built and some parts being in “bits and pieces,” NASA will have to decide on how they should be used, build additional instruments, launch them, and support the operations.
Reportedly, Grunsfeld and his secret team have come up with a plan to turn one of the telescopes to investigate the mysterious dark energy that is speeding up the expansion of the universe.
NASA officials stressed that they do not have a program or a budget to launch even one telescope at the moment, and that at the very earliest, under favorable budgets, it would be 2020 before even one of the two gifted telescopes could be ready for a mission.
The Washington Post asked Grunsfeld whether anyone at NASA was popping champagne, and he answered, “We never pop champagne here; our budgets are too tight.”
In the latest decadal survey the astronomical community had suggested a dark energy telescope as its top priority in astronomy and astrophysics, but the lack of funding – along with huge cost overruns by the James Webb Space Telescope — made it seem like such a telescope would be an impossibility.
The two telescopes could possibly be used for the proposed WFIRST project, which seemingly was not going anywhere with the latest budget proposal or as a ‘scout’ for the JWST.
“It would be a great discovery telescope for where Webb should look in addition to doing the work on dark energy,” Spergel said in the Washington Post.
Astronomers will be discussing the possibilities at a meeting at the National Academy of Sciences held on today in Washington, D.C. and how they could turn the two gifted telescopes into official missions.
This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)
Astronomers have known for years that our Milky Way and its closest neighbor, the Andromeda galaxy, (a.k.a M31) are being pulled together in a gravitational dance, but no one was sure whether the galaxies would collide head-on or glide past one another. Precise measurements from the Hubble Space Telescope have now confirmed that the two galaxies are indeed on a collision course, headed straight for a colossal cosmic collision.
No need to panic for the moment, as this is not going to happen for another four billion years. And while astronomers say it is likely the Sun will be flung into a different region of our galaxy, Earth and the solar system will probably just go along for the ride and are in no danger of being destroyed.
“In the ‘worst-case-scenario’ simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said team member Gurtina Besla of Columbia University in New York, N.Y. “The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies’ cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy.”
The simulations Besla was talking about came from precise measurements by Hubble, painstakingly determining the motion of Andromeda, looking particularly at the sideways motion of M31, which until now has not been able to be done.
“This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period,” said Jay Anderson of STScI.
Right now, M31 is 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.
Of course, the collision is not like a head-on between two cars that takes place in an instant. Hubble data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.
Astronomers said the stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.
There’s also the complication of M31’s small companion, the Triangulum galaxy, M33. This galaxy will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.
The astronomers working on this project said that they were able to make the precise measurements because of the upgraded cameras on Hubble, installed during the final servicing mission. This gave astronomers a long enough time baseline to make the critical measurements needed to nail down M31’s motion.
The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.
This series of photo illustrations shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy. Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger
First Row, Left: Present day. First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger. Second Row, Left: In 3.75 billion years Andromeda fills the field of view. Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation. Third Row, Left: In 3.9 billion years, star formation continues. Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped. Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes. Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.
Here’s a excellent video compilation featuring images from the Hubble Space Telescope, along with music by Kanye West and quotes from astronomers Neil deGrasse Tyson, Lawrence Krauss and Carl Sagan reflecting on our place in the Universe… and the Universe’s place within each of us.
Uploaded to YouTube by video editor Brandon Fibbs, this is a reminder of how Hubble has opened our eyes to the wonders of the cosmos. Enjoy.
“The cosmos is also within us. We’re made of star stuff… we are a way for the cosmos to know itself.”
– Carl Sagan
