This astounding mosaic of the Milky Way is comprised of 104 separate images and was taken in Elvas, Alentejo, Portugal by astrophotographer Miguel Claro. Visible is the arm of our galaxy the Milky Way, as well as many constellations like Cygnus, Cassiopeia, Sagittarius, and Scorpius. Look closely and find deep sky objects like Andromeda Galaxy. The image was taken in a portion of the Great Lake Alqueva Dark Sky Reserve in Portugal, a site designated as a “Starlight Tourism Destination.” The region has good atmospheric conditions for stargazing for more than 250 nights of the year, and special lodging is available just for astro-tourists.
This mosaic was taken on July 24, 2012, with a Canon 50D, 15 seg. a f/2.8, ISO 2000, Dist. Focal: 35 mm
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Swift J1745-26, with a scale of the moon as it would appear in the field of view from Earth. This image is from September 18, 2012 when the source peaked in hard X-rays. Credit: NASA/Goddard Space Flight Center/S. Immler and H. Krimm
Back in mid-September, the Swift satellite was going about its multi-wavelength business of watching for bursts of bright gamma-ray, X-ray, ultraviolet, or optical events in the sky, when it detected a rising tide of high-energy X-rays from a source toward the center of our Milky Way galaxy. But this was different from any other burst the satellite had detected, and after observing the event for a few days, astronomers knew this had to be a rare X-ray nova. What it meant was that Swift had detected the presence of a previously unknown stellar-mass black hole.
“Bright X-ray novae are so rare that they’re essentially once-a-mission events and this is the first one Swift has seen,” said Neil Gehrels from Goddard Space Flight Center, the mission’s principal investigator. “This is really something we’ve been waiting for.”
The object was named Swift J1745-26 after the coordinates of its sky position, the nova is located a few degrees from the center of our galaxy toward the constellation Sagittarius. While astronomers do not know its precise distance, they think the object resides about 20,000 to 30,000 light-years away in the galaxy’s inner region.
An X-ray nova is a short-lived X-ray source that appears suddenly in the sky and dramatically increases in strength over a period of a few days and then decreases, fading out over a few months. Unlike a conventional nova, where the compact component is a white dwarf, an X-ray nova is caused by material – usually gas — falling onto a neutron star or a black hole.
The rapidly brightening source triggered Swift’s Burst Alert Telescope twice on the morning of Sept. 16, and once again the next day.
Ground-based observatories detected infrared and radio emissions, but thick clouds of obscuring dust have prevented astronomers from catching Swift J1745-26 in visible light.
The nova peaked in hard X-rays — energies above 10,000 electron volts, or several thousand times that of visible light — on Sept. 18, when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant that serves as a calibration target for high-energy observatories and is considered one of the brightest sources beyond the solar system at these energies.
Even as it dimmed at higher energies, the nova brightened in the lower-energy, or softer, emissions detected by Swift’s X-ray Telescope, a behavior typical of X-ray novae. By Wednesday, Swift J1745-26 was 30 times brighter in soft X-rays than when it was discovered and it continued to brighten.
“The pattern we’re seeing is observed in X-ray novae where the central object is a black hole. Once the X-rays fade away, we hope to measure its mass and confirm its black hole status,” said Boris Sbarufatti, an astrophysicist at Brera Observatory in Milan, Italy, who currently is working with other Swift team members at Penn State in University Park, Pa.
Here’s usually happens in events like this: The black hole is part of a binary system with a normal Sun-like star. A stream of material flows into an accretion disk around the black hole. Usually, the disk of gas spirals in steadily to the black hole, heats up and produces a steady X-ray glow. But sometimes, for reasons unknown, the material is held up in the outer regions, held back by some mechanism, almost like a dam. Once enough gas accumulates, the dam breaks and a flood of gas surges towards the black hole, creating the X-ray nova outburst.
“Each outburst clears out the inner disk, and with little or no matter falling toward the black hole, the system ceases to be a bright source of X-rays,” said John Cannizzo, a Goddard astrophysicist. “Decades later, after enough gas has accumulated in the outer disk, it switches again to its hot state and sends a deluge of gas toward the black hole, resulting in a new X-ray outburst.”
This phenomenon, called the thermal-viscous limit cycle, helps astronomers explain transient outbursts across a wide range of systems, from protoplanetary disks around young stars, to dwarf novae — where the central object is a white dwarf star — and even bright emission from supermassive black holes in the hearts of distant galaxies.
It is estimated that our galaxy must harbor some 100 million stellar-mass black holes. Most of these are invisible to us, and only about a dozen have been identified.
Swift discovers about 100 bursts per year. The Burst Alert Telescope detects GRBs and other events and accurately determines their positions on the sky. Swift then relays a 3 arcminute position estimate to the ground within 20 seconds of the initial detection, enabling ground-based observatories and other space observatories the chance to observe the event as well. The Swift spacecraft itself “swiftly” –in less than approximately 90 seconds — and autonomously repoints itself to bring the burst location within the field of view of the sensitive narrow-field X-ray and UV/optical telescopes to observe the afterglow and gather data.
Artist's impression of the huge halo of hot gas surrounding the Milky Way Galaxy. Credit: NASA
Artist’s illustration of a hot gas halo enveloping the Milky Way and Magellanic Clouds (NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A.Gupta et al.)
Our galaxy — and the nearby Large and Small Magellanic Clouds as well — appears to be surrounded by an enormous halo of hot gas, several hundred times hotter than the surface of the Sun and with an equivalent mass of up to 60 billion Suns, suggesting that other galaxies may be similarly encompassed and providing a clue to the mystery of the galaxy’s missing baryons.
In the artist’s rendering above our Milky Way galaxy is seen at the center of a cloud of hot gas. This cloud has been detected in measurements made with Chandra as well as with the European Space Agency’s XMM-Newton space observatory and Japan’s Suzaku satellite. The illustration shows it to extend outward over 300,000 light-years — and it may actually be even bigger than that.
While observing bright x-ray sources hundreds of millions of light-years distant, the researchers found that oxygen ions in the immediate vicinity of our galaxy were “selectively absorbing” some of the x-rays. They were then able to measure the temperature of the halo of gas responsible for the absorption.
The scientists determined the temperature of the halo is between 1 million and 2.5 million kelvins — a few hundred times hotter than the surface of the Sun.
But even with an estimated mass anywhere between 10 billion and 60 billion Suns, the density of the halo at that scale is still so low that any similar structure around other galaxies would escape detection. Still, the presence of such a large halo of hot gas, if confirmed, could reveal where the missing baryonic matter in our galaxy has been hiding — a mystery that’s been plaguing astronomers for over a decade.
Unrelated to dark matter or dark energy, the missing baryons issue was discovered when astronomers estimated the number of atoms and ions that would have been present in the Universe 10 billion years ago. But current measurements yield only about half as many as were present 10 billion years ago, meaning somehow nearly half the baryonic matter in the Universe has since disappeared.
Recent studies have proposed that the missing matter is tied up in the comic web — vast clouds and strands of gas and dust that surround and connect galaxies and galactic clusters. The findings announced today from Chandra support this, and suggest that the missing ions could be gathered around other galaxies in similarly hot halos.
Even though previous studies have indicated halos of warm gas existing around our galaxy as well as others, this new research shows a much hotter, much more massive halo than ever detected.
“Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way,” said study co-author Smita Mathur of Ohio State University in Columbus. “It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large.”
Read the full news release from NASA here, and learn more about the Chandra mission here. (The team’s paper can be found on arXiv.org.)
NOTE: the initial posting of this story mentioned that this halo could be dark matter. That was incorrect and not implied by the actual research, as dark matter is non-baryonic matter while the hot gas in the halo is baryonic — i.e., “normal” — matter. Edited. – JM
Caption: Fully integrated Gaia payload module with nearly all of the multilayer insulation fabric installed. Credit: Astrium SAS
Earlier this month ESA’s Gaia mission passed vital tests to ensure it can withstand the extreme temperatures of space. This week in the Astrium cleanroom at Intespace in Toulouse, France, had it’s payload module integrated, ready for further testing before it finally launches next year. This is a good opportunity to get to know the nuts and bolts of this exciting mission that will survey a billion stars in the Milky Way and create a 3D map to reveal its composition, formation and evolution.
Gaia will be operating at a distance of 1.5 million km from Earth (at L2 Lagrangian point, which keeps pace with Earth as we orbit the Sun) and at a temperature of -110°C. It will monitor each of its target stars about 70 times over a five-year period, repeatedly measuring the positions, to an accuracy of 24 microarcseconds, of all objects down to magnitude 20 (about 400,000 times fainter than can be seen with the naked eye) This will provide detailed maps of each star’s motion, to reveal their origins and evolution, as well as the physical properties of each star, including luminosity, temperature, gravity and composition.
The service module houses the electronics for the science instruments and the spacecraft resources, such as thermal control, propulsion, communication, and attitude and orbit control. During the 19-day tests earlier this month, Gaia endured the thermal balance and thermal-vacuum cycle tests, held under vacuum conditions and subjected to a range of temperatures. Temperatures inside Gaia during the test period were recorded between -20°C and +70°C.
“The thermal tests went very well; all measurements were close to predictions and the spacecraft proved to be robust with stable behavior,” reports Gaia Project Manager Giuseppe Sarri.
For the next two months the same thermal tests will be carried out on Gaia’s payload module, which contains the scientific instruments. The module is covered in multilayer insulation fabric to protect the spacecraft’s optics and mirrors from the cold of space, called the ‘thermal tent.’
Gaia contains two optical telescopes that can precisely determine the location of stars and analyze their spectra. The largest mirror in each telescope is 1.45 m by 0.5 m. The Focal Plane Assembly features three different zones associated with the science instruments: Astro, the astrometric instrument that detects and pinpoints celestial objects; the Blue and Red Photometers (BP/RP), that determines stellar properties like temperature, mass, age, elemental composition; and the Radial-Velocity Spectrometer (RVS),that measures the velocity of celestial objects along the line of sight.
The focal plane array will also carry the largest digital camera ever built with, the most sensitive set of light detectors ever assembled for a space mission, using 106 CCDs with nearly 1 billion pixels covering an area of 2.8 square metres
After launch, Gaia will always point away from the Sun. L2 offers a stable thermal environment, a clear view of the Universe as the Sun, Earth and Moon are always outside the instruments’ fields of view, and a moderate radiation environment. However Gaia must still be shielded from the heat of the Sun by a giant shade to keep its instruments in permanent shadow. A ‘skirt’ will unfold consisting of a dozen separate panels. These will deploy to form a circular disc about 10 m across. This acts as both a sunshade, to keep the telescopes stable at below –100°C, and its surface will be partially covered with solar panels to generate electricity.
Once testing is completed the payload module will be mated to the service module at the beginning of next year and Gaia will be launched from Europe’s Spaceport in French Guiana at the end of 2013.
Here’s a wonderful new timelapse from photographer John Ecklund, a photographer from Portland, Oregon. He captures incredible views of the Milky Way over Crater Lake, Mount Hood, Mount St. Helens, the Painted Hills and more, even nabbing a few meteors and a pass of the International Space Station.
“I choose to shoot locations that appeal to the way I would like to interpret the story of time,” says Ecklund. “Here in the Pacific Northwest, there are endless opportunities to document the magnificence of the world around us. I have discovered that when time is the storyteller, a special kind of truth emerges.” Continue reading “Beautiful Timelapse: Purely Pacific Northwest”
This image shows one of the two ‘exact matches’ to the Milky Way system found in a new survey. The larger galaxy, denoted GAMA202627, which is similar to the Milky Way clearly has two large companions off to the bottom left of the image. InImage Credit: Dr Aaron Robotham, ICRAR/St Andrews using GAMA data.
Here’s something astronomers haven’t seen before: galaxies that look just like our own Milky Way. It’s not that our spiral-armed galaxy is rare but instead the whole neighborhood in which we reside seems to be unusual. Until now, a galaxy paired with close companions like the Magellanic Clouds has not been found elsewhere. But using data from a new radio astronomy survey, astronomers found two Milky Way look-alikes and several others that were similar.
“We’ve never found another galaxy system like the Milky Way before, which is not surprising considering how hard they are to spot!” said Dr. Aaron Robotham with the International Centre for Radio Astronomy Research (ICRAR). “It’s only recently become possible to do the type of analysis that lets us find similar groups.”
“Everything had to come together at once,” Robotham added. “We needed telescopes good enough to detect not just galaxies but their faint companions, we needed to look at large sections of the sky, and most of all we needed to make sure no galaxies were missed in the survey.”
Robotham presented his new findings at the International Astronomical Union General Assembly in Beijing this week.
Using what astronomer consider the most detailed map of the local Universe yet — the Galaxy and Mass Assembly survey (GAMA) — Robotham and his colleagues found that although companions like the Magellanic Clouds are rare, when they are found they’re usually near a galaxy very like the Milky Way, meaning we’re in just the right place at the right time to have such a great view in our night sky.
“The galaxy we live in is perfectly typical, but the nearby Magellenic Clouds are a rare, and possibly short-lived, occurrence. We should enjoy them whilst we can, they’ll only be around for a few billion more years,” said Robotham.
Astronomers have used computer simulations of how galaxies form and they don’t produce many examples similar to the Milky Way and its surroundings, so they have predicted them to be quite a rare occurrence. Astronomers they really haven’t been able to tell just how rare they are, until now, using the new survey which looks at hundreds of thousands of galaxies.
“We found about 3% of galaxies similar to the Milky Way have companion galaxies like the Magellanic Clouds, which is very rare indeed,” Robotham said. “In total we found 14 galaxy systems that are similar to ours, with two of those being an almost exact match.”
The Milky Way is locked in a complex cosmic dance with its close companions the Large and Small Magellanic Clouds, which are clearly visible in the southern hemisphere night sky. Many galaxies have smaller galaxies in orbit around them, but few have two that are as large as the Magellanic Clouds.
Robotham and his team will continue searching for more Milky Way twin systems.
The paper “Galaxy and Mass Assembly (GAMA): In search of Milky-Way Magellanic Cloud Analogues” can be read here or (free version) at arXiv
Last week we posted an astrophoto by Jack Fusco, and when I looked at more of his images, this one just absolutely blew me away! Jack took a trip to Acadia National Park in Maine, USA, and his night sky images from that location are just gorgeous. “It’s amazing to me that every single person in Acadia isn’t awake the entire night out stargazing,” Jack said on Google+ . “The amount of stars is just absolutely incredible here and I could not have asked for any better conditions.”
Of this image, Jack said, “It’s important to not just worry about the destination, but to notice all of the things that we go through on our path there,” and then quoted musician Frank Turner: “We’re going nowhere slowly, but we’re seeing all the sights.”
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Photographer Mike Salway recently took a trip to the western Australia Kimberly Region of the Outback, and has posted some amazing night sky images of his adventures. This picture — and the name of the geologic features — especially caught my eye. The Bungle Bungles of Purnululu National Park are an incredible sight in themselves, huge beehive-shaped sandstone formations. But Mike was able to take a panoramic view of the Milky Way arching over the formations, a symmetrical halo of light in the full sky.
“You know the skies are dark when you can see the Milky Way overhead, even when there’s a more than half-moon shining brightly high in the west sky,” Mike wrote on his website. “And that’s what it was like at the Bungle Bungles.”
This image is an 8 frame panorama, taken on the Piccaninny Creek bed with his Canon 5D Mk II and Samyang 14mm f/2.8 lens.
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Caption: ‘The Lookout’ – Bass Harbor Lighthouse – Acadia National Park, Maine. Credit: Jack Fusco.
This gorgeous shot of the Bass Harbor Lighthouse — seemingly on the lookout for the Milky Way — almost got away from astrophotographer Jack Fusco, but luckily he had a backup plan!
Jack’s description of the photo:
This was the shot that almost got away. I had this in mind and planned out well before I had arived in Acadia. Before the Milky Way was in place on my first visit, the sky was covered by almost the only clouds I saw all trip. A change in forecast for the night before my drive back to New Jersey gave me one last chance to capture it. I set up to take some star trails while waiting for everything to be in position only to have my battery die moments before I took this. Luckily, I had a fully charged backup battery in my bag. I ran to grab it, set back up and started to shoot again. Sitting out under the stars and listening to the water crash against the rocks was an experience that words can not do justice.
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Ah, the good life! “Probably one of my favorite things to do is sit outside underneath the stars,” said astrophotographer Harley Grady from Texas, who took this self- and galactic-portrait on June 19, 2012. Grady said this is a single 30 second exposure, with a red LED light to illuminate himself and 6″ Dob telescope.
How many of our other readers could take a similar picture of themselves?
Shot with a Nikon D700,Tokina 16-28mm f2.8 Lens, ISO 3200, WB 4000K.
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Image caption: Galactic Relaxing. Credit and copyright: Harley Grady 2012
