A view of the ISS from a Soyuz spacecraft while space shuttle Endeavour was docked. Credit: NASA/ESA
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The six crewmembers on board the International Space Station were told to take shelter in the two Russian Soyuz spacecraft early Tuesday because Space Command predicted a piece of space junk could make a close approach to the station. Radar tracking indicated the debris would make its close pass at 8:08 a.m. EDT (12:08 UTC), coming within about 243 meters (800 feet) of the station and well within the “pizza box” -shaped area around the ISS, but when no impact was detected the crew was told they could reenter the station and resume normal operations.
NASA’s Chief Scientist for Orbital Debris Nicholas L. Johnson told Universe Today during a previous “conjuction” of space debris and the ISS that on average, close approaches to ISS occur about three times a month. An approach of debris is considered “close” only when it enters an imaginary “pizza box” shaped region around the station, measuring 0.75 kilometers above and below the station and 25 kilometers on each side( 2,460 feet above and below and 15.6 by 15.6 miles).
Johnson said that small pieces of debris have already collided with ISS on many occasions, but these debris to date have not affected the safety of the crew or the operation of the mission. “The dedicated debris shields on ISS can withstand particles as large as 1 cm in diameter,” he said.
The piece of space junk was detected too late for the station to perform an evasive maneuver, so the crew was told to “shelter in place” on the two Soyuz spacecrafts. The crew on board is commander Andrey Borisenko, Alexander Samokutyaev and Ronald Garan, who took shelter aboard the Soyuz TMA-21 spacecraft docked to the Poisk module, and Sergei Volkov, Michael Fossum and Furukawa who went on to the Soyuz TMA-02M spacecraft docked to the Rassvet module.
This false color satellite image shows active lava flows of the Nabro volcano in Eritrea on June 24, 2011. Credit: the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite.
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Wow! What an amazing and detailed top-down view of an active volcano! This is the Nabro Volcano, which has been erupting since June 12, 2011. It sits in an isolated region on the border between Eritrea and Ethiopia and satellite remote sensing is currently the only reliable way to monitor the ongoing eruption, according to the NASA Earth Observatory website. The bright red portions of the false-color image (above) indicate hot surfaces. See below for a zoomed-in look. Both images were taken by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite.
This natural-color image shows a close-up view of the volcanic plume and eruption site of the Nabro volcano. Credit: the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite
Robert Simmon of the NASA Earth Observatory website describes the scenes:
Hot volcanic ash glows above the vent, located in the center of Nabro’s caldera. To the west of the vent, portions of an active lava flow (particularly the front of the flow) are also hot. The speckled pattern on upstream portions of the flow are likely due to the cool, hardened crust splitting and exposing fluid lava as the flow advances. The bulbous blue-white cloud near the vent is likely composed largely of escaping water vapor that condensed as the plume rose and cooled. The whispy, cyan clouds above the lava flow are evidence of degassing from the lava.
The natural-color image (lower) shows a close-up view of the volcanic plume and eruption site. A dark ash plume rises directly above the vent, and a short, inactive (cool) lava flow partially fills the crater to the north. A gas plume, rich in water and sulfur dioxide (which contributes a blue tint to the edges of the plume) obscures the upper reaches of the active lava flow. Black ash covers the landscape south and west of Nabro.
Limited reports from the region say that at least 3,500 people and up to 9,000 that have been affected by the eruption, with at least 7 deaths caused by the erupting volcano. The ash plume has also disrupted flights in the region.
Dan Linehan's recent offering entitled "Burt Rutan's Race to Space" is a concise, yet detailed, accounting of how one man revolutionized air and space travel. Photo Credit: Zenith Press
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Voyager, Proteus and SpaceShipOne have become aerospace legends. As has the man who established them all – Burt Rutan. Zenith Press has released a chronicle of the man and his machines entitled Burt Rutan’s Race to Space: The Magician of Mojave and His Flying Innovations. The book provides a chronicle of all the air and spacecraft that have soared off of Rutan’s blueprints and into reality.
The book’s first main segment is a large section which is essentially a catalog of the numerous craft that Rutan has produced over the decades. Many of the flying machines have their unique characteristics highlighted within the 160 pages of this book. Fear not, this tome is wallpapered with images – most of which are color (175 color images to 55 black and white).
SpaceShipOne now hangs in the Smithsonian's Air & Space Museum in Washington D.C. - between the Spirit of St. Louis and the Bell X-1. Photo Credit: Scaled Composites
Some of the most interesting of these images are not the glossy stills of air or spacecraft in action but rather the simple drawings that are done by the man himself. These sketches, some little more than cartoons others just simplistic line-drawings, highlight the genius that is Rutan and provide an insight into how his mind works.
The nature of the book changes somewhat when one reaches the chapter entitled, “The Scaled Composites Years.” From this point on, the book’s focus narrows to concentrate on Rutan’s X-PRIZE efforts – and beyond.
Rutan's dreams of flight started at an early age. He was a child when he first began crafting airplanes out of wood. Photo Credit: Virgin Galactic
The book was written by Dan Linehan and is his second detailing the efforts of Rutan and Scaled Composites (the first was SpaceShipOne: An Illustrated History). In short, the freelance writer is steeped in all things Rutan. Whereas his first work on the subject covered the history-making flight of SpaceShipOne, this effort is a general overview of Rutan and his legacy. But be forewarned, there are many projects that span the entire realm of aerospace that Rutan and company have been involved with that might surprise you.
Given that the Mojave “magician” has retired recently – this book is timely, enjoyable and acts as a wonderful window into the mind of the man that has revolutionized flight. SpaceShipTwo continues to successfully complete test after test – making Burt Rutan’s Race to Space a primer for things to come. The book retails for $30, and it is well-worth the price and will be a welcome addition to any space buff’s collection.
SpaceShipTwo being carried underneath White Knight Two is currently being tested in preparation to send average citizens into suborbital space. Photo Credit: Virgin Galactic
Animation of 2011 MD on Monday, June 27, 2011 at 09:30 UTC. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South. Click for original larger version.
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Today, Monday June 27 at about 17:00 UT, asteroid designated as 2011 MD will pass only 12,300 kilometers (7,600 miles) above the Earth’s surface. Here are some images and an animation of the asteroid’s close approach taken around 09:30 UT taken by Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South through a 2.0-m f/10.0 Ritchey-Chretien and a CCD. The trio of astronomers say that at the time these images were taken, the asteroid had a magnitude of about 14.5. At the moment of its close approach, 2011 MD will be bright as magnitude ~11.8.
The animation above shows the object’s movement in the sky. Each image was 20-second exposure.
See more below from Guido, Howes and Sostero.
Below is a single 20-second exposure also taken by the 2 meter telescope at Faulkes Telescope South, and just below that is another image using a RGB filter.
2011 MD on Monday, June 27, 2011 at 09:30 UTC. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South2011 MD on Monday, June 27, 2011 at 09:30 UTC with RBG filter. Credit: Ernesto Guido, Nick Howes and Giovanni Sostero at the Faulkes Telescope South.
Some early observers have suggested that 2011 MD — which is only 5-20 meters in diameter — could possibly be a piece of space junk, such as a rocket booster. However, additional observations and further calculations show that this asteroid could not have been close enough to Earth any time during the space age to have started off as a rocket booster.
Trajectory of 2011 MD from the general direction of the Sun. Credit: NASA
Again, scientists at NASA’s Asteroid Watch program at JPL say there is no danger of the asteroid hitting Earth. “There is no chance that 2011 MD will hit Earth but scientists will use the close pass as opportunity to study it w/ radar observations,” they said on the the @AsteriodWatch Twitter feed. “Asteroid 2011 MD measures about 10 meters. Stony asteroids less than 25 m would break up in Earth’s atmosphere and not cause ground damage.”
NASA's Shuttle Launch Director Mike Leinbach has been with NASA since 1984 and took a moment to share his thoughts about the future. Photo Credit: Jason Rhian
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CAPE CANAVERAL Fla. – He has been with the shuttle program for the past three decades and has witnessed both its tragedies and its triumphs. NASA’s Shuttle Launch Director Mike Leinbach reflected on the end of the shuttle era when interviewed this week. He talked a bit about his plans for the future as well as what he thinks people can expect from both him and his team on launch day.
Q: The Terminal Countdown Demonstration Test (TCDT) for STS-135 has just wrapped up, is this is a period of accelerated work for you and your team or is this a time when you can catch your breath?
Leinbach: “This TCDT was a little different; we had a very busy period getting the crew
ready for this mission. On July 4 we’ll have a bit of a break and then things
will pick right back up again as we get ready for launch.”
Q: What do you think you will be feeling when that final launch occurs?
Leinbach: “I don’t know, I mean I have thought a lot about this…I don’t know what it’s
going to be like. For the last flight of Discovery we had one more launch for
both Endeavour and Atlantis, well now this really and truly the last flight of
the shuttle program… so it’s going to be a very reflective time.”
Leinbach gestures toward his former secretary before the start of the interview. Photo Credit: Jason Rhian
Q: Do you think anything will be special about this mission?
Leinbach: “The launch itself will be very much any other launch. When the guy’s are
working on the consoles they are very serious about what they are doing.
They won’t be distracted by the fact that it is the last one.
Q: Speaking of your job – it keeps you very busy, have you had any time to reflect?
Leinbach: “For the moment I still have a lot to do concluding TCDT, but this Saturday I
am planning on driving out to the launch pad and just looking up at Atlantis
and just soaking it all in, all by myself.”
Leinbach started working for NASA as a structural engineer in 1984, his words are softly spoken which tends to lend them even more weight. His first mission as launch director was STS-114. This was the first shuttle launch after the loss of the space shuttle Columbia in 2003. Leinbach led the recovery team searching for Columbia’s debris in Texas. A year later in 2004 Leinbach was awarded the Presidential Rank Award, which is given in recognition of long-term accomplishments.
Atlantis will carry the four person crew of STS-135 to the International Space Station on a resupply flight designed to keep the orbiting outpost well stocked after the shuttles are decommissioned. The mission is scheduled to last twelve days, launching on July 8 at 11:26 a.m. EDT. The crew consists of Commander Chris Ferguson, Pilot Doug Hurley and Mission Specialists Sandra Magnus and Rex Walheim.
The Launch Control Center or LCC is where the final "go" "no-go" for launch is determined. Photo Credit: Jason Rhian
STS-135 crew at TCDT Q&A session with journalists at base of Launch Pad 39A, Kennedy Space Center. From left; Mission Specialists Rex Walheim and Sandy Magnus; Pilot Doug Hurley and Commander Chris Ferguson
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KENNEDY SPACE CENTER – The “Final Four” shuttle astronauts who will ever voyage to Earth orbit aboard a NASA Space Shuttle Orbiter jetted into the Kennedy Space Center (KSC) this week for their final simulated countdown training at the seaside Florida Launch Pad.
The all veteran crew for the STS-135 mission arrived at Kennedy’s Shuttle Landing Facility (SLF) on twin T-38 jets for four days of comprehensive flight training for what’s known as the Terminal Countdown Demonstration Test (TCDT). Along with all other shuttle flight related activities, it’s the very last time this training will ever occur.
The TCDT is part of the ritual of training for all shuttle crews that takes place in the last few weeks preceding a liftoff and that concludes with a full countdown dress rehearsal from inside Atlantis at the launch pad.
The last ever shuttle crew jets into KSC for TCDT training at KSC aboard T-38 jets. From left; Sandy Magnus, Doug Hurley, Commander Chris Ferguson and Rex Walheim. Credit: Ken Kremer
Chris Ferguson is leading the STS-135 mission and he will be recorded in history as the final Space Shuttle Commander. This will be Ferguson’s third shuttle flight and second one as Commander. Also aboard are Pilot Doug Hurley and Mission Specialists Sandy Magnus and Rex Walheim.
The quartet of space flyers are due to blast off aboard Space Shuttle Atlantis on July 8 at 11:26 a.m. EDT for the “Grand Finale” of NASA’s thirty year old Space Shuttle Program. If all goes according to plan the end of the Shuttle Era is less than 1 month away.
It’s a bittersweet moment for everyone working on the shuttle program. Proud to be part of a magnificent adventure with the most complicated machine ever built by humans, but simultaneously sad that the program is ending well before its true flight time is up and with no concrete timetable to replace the trio of majestic spaceships.
“We are incredibly proud to represent this, the final flight,” said STS-135 Commander Chris Ferguson after touchdown to dozens and dozens of journalists gathered at the shuttle landing strip to greet the astronauts.
“I speak on behalf of the crew, everyone in the astronaut office, and I’m sure everybody here at KSC in saying that we are just trying to savor the moment,” Ferguson added. “As our children and our children’s children ask us, we want to be able to say, ‘We remember when there was a space shuttle.”
The first order of business for Ferguson and Hurley was to practice shuttle landings in the Shuttle Training Aircraft (STA), which is a modified Gulfstream II jet.
During the TCDT period, the crew engaged in mission briefings at the Launch Control Center which is the brain of shuttle launch operations, payload familiarization and training at the Space Station Processing Facility, fire suppression training, range safety and security briefings and emergency escape training in an M113 armored personnel carrier near Launch Pad 39A. Read more in my upcoming features.
On the last day of TCDT, the astronauts donned their orange launch and entry suits, journeyed to the pad in the Astrovan and were strapped to their assigned seated inside the orbiter exactly as will occur on launch day for a full dress rehearsal of the launch countdown.
STS-135 Crew at TCDT pad emengency training at Pad 39A. From left are Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialists Sandy Magnus and Rex Walheim. Credit: NASA/Kim Shiflett
The crew also met with over 100 reporters for a Q & A session at the base of Launch Pad 39A which was back dropped by a thrilling view of Shuttle Atlantis atop the Mobile Launch Platform and the gigantic Flame Duct which directs the rocket exhaust way from the shuttle stack during launch.
“We’re very honored to be in this position,” Ferguson said to reporters at the foot of the pad. “There are many people who could be here. When the dice fell our names were facing up. We consider ourselves fortunate and lucky.”
“I think each of us feels a little extra burden to make sure we put on the best possible face forward for the last go around of this. The crew’s very prepared and we’re going to do a fantastic job.”
“I don’t think that the full magnitude of the moment will really hit us until the wheels have stopped on the runway,” said Ferguson, reflecting on the significance of the grand finale of all shuttle missions. “I’m not sure words will really be able to capture for the crew and for the entire shuttle workforce just how much the shuttle program has meant to us for the last 30 years.”
“TDCT is very comprehensive, hands on and invaluable training at the place you’re going to do it,” said Hurley. “Everything is a just a little bit different when you are in the real vehicle so this is a great way to get you ready for launch day – when it counts!”
Tucked inside Atlantis cargo bay is the Italian- built “Raffaello” logistics module, the primary payload. Raffaello is loaded full with some five tons of critical spare parts, crew supplies and science experiments that will be delivered to the International Space Station (ISS) during the 12 day flight.
The secondary payload is the Robotic Refueling Mission (RRM) which will demonstrate tools and techniques to refuel satellites in orbit.
The STS-135 crew arrive at KSC aboard a wave of T-38 jets for countdown, payload and emergency training. Credit: Ken Kremer
“Sandy Magnus is our ‘transfer czar’ in charge of emptying and filling Raffaello,” said Ferguson. Magnus is an ideal choice for the mission since she lived for months aboard the orbiting outpost and is familiar with its nook and crannies.
“We feel very honored to be on this flight and are very focused to perform it well,” said Magnus. “We are just the tip of the iceberg of a huge group of people who plan and get the hardware ready and prepare all our procedures.”
“I often think about how we will launch from the exact same launch pad that Apollo 11 launched at to go to the moon. It gives you goose bumps,” said Walheim.
Media with STS-135 astronuats at TCDT Q&A session at Launch Pad 39A. Credit: Ken Kremer
Accomplished amateur astronomer and blogger Peter Lake, a.k.a “AstroSwanny” from Australia captured some of the first images of what will be a very close pass of Earth by asteroid 2011 MD. He actually took the image at 07:00 UTC on June 26th with a 20 inch telescope in New Mexico controlled via his iPhone, through the Global Rent-A-Scope program. Ahh, the wonders of technology! As Peter says, “Its not every day, that an asteroid misses by less than 3-5 earth Radii.”
The asteroid, which was only detected last week, is about 25 to 55 feet (8 to 18 m) across, is expected to pass less than 8,000 miles above Earth’s surface around 1 p.m. EDT (17:00 UT) on Monday, June 27th. The time of closest approach will be observable from South Africa and parts of Antarctica, but the approach will be visible across Australia, New Zealand, southern and eastern Asia, and the western Pacific.
Below is a video he compiled of the his observations of the pass, and used ten 120-second images for the video.
Peter also noted that “Its close approach is being followed with great interest, more for honing the skills and techniques of the Minor Planet Center and the network of asteroid hunting astronomers, rather than because it poses any real danger.”
Thanks to Peter and his Aartscope Blog for sharing these views with Universe Today.
Thousands of galaxies observed by the Herschel Space Observatory through the Lockman hole. Credit: ESA.
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You’ve probably heard of the cosmic microwave background, but it doesn’t stop there. The as-yet-undetectable cosmic neutrino background is out there waiting to give us a view into the first seconds after the Big Bang. Then, looking further forward, there are other backgrounds across the electromagnetic spectrum – all of which contribute to what’s called the extragalactic background light, or EBL.
The EBL is the integrated whole of all light that has ever been radiated by all galaxies across all of time. At least, all of time since stars and galaxies first came into being – which was after the dark ages that followed the release of the cosmic microwave background.
The cosmic microwave background was released around 380,000 years after the Big Bang. The dark ages may have then persisted for another 750 million years, until the first stars and the first galaxies formed.
In the current era, the cosmic microwave background is estimated to make up about sixty percent of the photon density of all background radiation in the visible universe – the remaining forty per cent representing the EBL, that is the radiation contributed by all the stars and galaxies that have appeared since.
This gives some indication of the enormous burst of light that the cosmic microwave background represented, although it has since been red-shifted into almost invisibility over the subsequent 13.7 billion years. The EBL is dominated by optical and infrared backgrounds, the former being starlight and the latter being dust heated by that starlight which emits infrared radiation.
Just like the cosmic microwave background can tell us something about the evolution of the earlier universe, the cosmic infrared background can tell us something about the subsequent evolution of the universe – particularly about the formation of the first galaxies.
The power density of the universe's background radiation plotted over wavelength. The cosmic microwave background, though substantially red-shifted due to its age, still dominates. The remainder, extragalactic background light, is dominated by optical and infrared radiation, which have power densities several orders of magnitude higher than the remaining radiation wavelengths.
The Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe is a ‘guaranteed time’ project for the Herschel Space Observatory. Guaranteed means there always a certain amount of telescope time dedicated to this project regardless of other priorities. The PACS Evolutionary Probe project, or just PEP, aims to survey the cosmic infrared background in the relatively dust free regions of the sky that include: the Lockman Hole; the Great Observatories Origins Deep Survey (GOODS) fields; and the Cosmic Evolution Survey (COSMOS) field.
The Herschel PEP project is collecting data to enable determination of rest frame radiation of galaxies out to a redshift of about z =3, where you are observing galaxies when the universe was about 3 billion years old. Rest frame radiation means making an estimation of the nature of the radiation emitted by those early galaxies before their radiation was red-shifted by the intervening expansion of the universe.
The data indicate that infrared contributes around half of the total extragalactic background light. But if you just look at the current era of the local universe, infrared only contributes one third. This suggests that more infrared radiation was produced in the distant past, than in the present era.
This may be because earlier galaxies had more dust – while modern galaxies have less. For example, elliptical galaxies have almost no dust and radiate almost no infrared. However, luminous infrared galaxies (LIRGs) radiate strongly in infrared and less so in optical, presumably because they have a high dust content.
Modern era LIRGs may result from galactic mergers which provide a new supply of unbound dust to a galaxy, stimulating new star formation. Nonetheless, these may be roughly analogous to what galaxies in the early universe looked like.
Dustless, elliptical galaxies are probably the evolutionary end-point of an galactic merger, but in the absence of any new material to feed off these galaxies just contain aging stars.
So it seems that having a growing number of elliptical galaxies in your backyard is a sign that you live in a universe that is losing its fresh, infrared flush of youth.
NASA's Mars Science Laboratory Curiosity rover. Curiosity is a mobile robot for investigating Mars' past or present ability to sustain microbial life. Curiosity is being tested in preparation for launch in the fall of 2011. The mast, or rover's "head," rises to about 2.1 meters (6.9 feet) above ground level, about as tall as a basketball player. This mast supports two remote-sensing instruments: the Mast Camera, or "eyes," for stereo color viewing of surrounding terrain and material collected by the arm; and, the ChemCam instrument, which is a laser that vaporizes material from rocks up to about 9 meters (30 feet) away and determines what elements the rocks are made of. Credit: NASA/JPL-Caltech. New NASA High Resolution Curiosity Animations below
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NASA’s next Mars rover, the Curiosity Mars Science Laboratory, will soon embark on a quantum leap in humankind’s scientific exploration of the Martian surface -the most Earthlike planet in our Solar System.
To get a birds eye understanding of Curiosity’s magnificent capabilities, check out the dramatic new high resolution animation below which depicts NASA’s next Mars rover traversing tantalizing terrain for clues to whether Martian microbial life may have existed, evolved and been sustained in past or present times.
The new action packed animation is 11 minutes in length. It depicts sequences starting with Earth departure, smashing through the Martian atmosphere, the nail biting terror of the never before used rocket-backpack sky crane landing system and then progressing through the assorted science instrument capabilities that Curiosity will bring to bear during its minimum two year expedition across hitherto unseen and unexplored Martian landscapes, mountains and craters.
Curiosity is equipped with 10 science instruments. The three meter long robot is five times the weight of any previous Mars rover.
Those who closely follow the adventures of NASA’s Spirit and Opportunity rovers, like myself, will quickly recognize several of the panoramic scenes which have been included to give a realistic feeling of vistas to expect from the car sized Curiosity rover.
Here is a shorter 4 minute animation with expert narration
Along the way you’ll experience Curiosity zapping rocks with a laser, deftly maneuvering her robotic arm and camera mast and retrieving and analyzing Martian soil samples.
“It is a treat for the 2,000 or more people who have worked on the Mars Science Laboratory during the past eight years to watch these action scenes of the hardware the project has developed and assembled,” said Mars Science Laboratory Project Manager Pete Theisinger at NASA’s Jet Propulsion Laboratory, Pasadena, Calif, in a NASA statement. “The animation also provides an exciting view of this mission for any fan of adventure and exploration.” Curiosity - The Next Mars Rover analyzes Martian rocks
Curiosity rover examines a rock on Mars with a set of tools at the end of the rover's arm, which extends about 2 meters (7 feet). Two instruments on the arm can study rocks up close. Also, a drill can collect sample material from inside of rocks and a scoop can pick up samples of soil. The arm can sieve the samples and deliver fine powder to instruments inside the rover for thorough analysis. Credit: NASA/JPL-Caltech
Curiosity was flown this week from her birthplace at NASA’s Jet Propulsion Laboratory in California to her future launch site in Florida aboard a C-17 military cargo transport aircraft.
She arrived at the Shuttle Landing Facility (SLF) at the Kennedy Space Center on June 22. The SLF is the same landing strip where I watched the STS-135 crew arrive for NASA’s final shuttle mission just days earlier days for their final launch countdown training.
NASA has scheduled Curiosity to blast off for the red planet on Nov. 25, 2011 from Cape Canaveral Air Force Station aboard an Atlas V rocket. Curiosity will touchdown in August 2012 at a landing site that will be announced soon by Ed Weiler, NASA Associate Administrator for the Science Mission Directorate in Washington, D.C. Curiosity rover traverses new Martian terrain in search of habitats for microbial life. Credit: NASA/JPL-Caltech
The spiral galaxy M33 is one of the largest galaxies in our local group. This spiral galaxy is moderately tilted when viewed from Earth, displaying a lack of a distinct central bulge but prominent spiral arms. It has only one potential companion galaxy (the Pisces Dwarf) and its spiral arms are so pristine, they have been thought to be unperturbed by the accretion of dwarf galaxies that constantly occurs in the Milky Way and Andromeda galaxy. Yet these features are what has made M33 so hard to explain. Since larger galaxies are expected to form from the merger of smaller galaxies it is expected that M33 should show some scars from previous mergers. If this picture is true, where are they?
The role of galaxy accretion in our own galaxy was first revealed in 1994 with the discovery of the Sagittarius stellar stream. With the completion of the first Sloan Digitised Sky Survey, many more tidal streams were revealed in our own galaxy. Modeling of the kinematics of these streams suggested they should last billions of years before fading into the rest of the galaxy. Deep imaging of the Andromeda galaxy revealed stellar streams as well as a notable warping of the disc of the galaxy.
Yet M33 seems to lack obvious signs of these structures. In 2006, a spectroscopic study analyzed the bright red giants in the galaxy and found three distinct populations. One could be attributed to the disc, one to the halo, but the third was not immediately explicable. Could this be the relic of an ancient satellite?
Another potential clue on missing mergers was discovered in 2005 when a radio survey around M33 was conducted with the Arecibo telescope. This study uncovered large clouds with a thousand to a million solar masses worth of raw hydrogen suspended around the galaxy. Might these be incomplete dwarf galaxies that never merged into M33? A new study uses the Subaru telescope atop Mauna Kea to study these regions as well as the outskirts of M33 to better understand their history.
The team, led by Marco Grossi at the Observatório Astronómico de Lisboa in Portugal, did not find evidence of a stellar population in these clouds suggesting they were not likely to be galaxies in their own right. Instead, they suggest that these clouds may be analogous to hydrogen clouds around the Milky Way and Andromeda which are “often found close to stellar streams or disturbances in the stellar disc” where gas is pulled from a former satellite galaxy through tidal or ram-pressure stripping. This would constitute another piece of indirect evidence that M33 once underwent mergers of some sort.
Outside of these clouds, in the outskirts of the galaxy, the team uncovered a diverse population of stars beyond the main disc. The overall metallicity of these stars was lower, but it also included some younger stars. At such a distance, these young stars would not be expected unless accreted.
While this finding doesn’t fully answer the question of how M33 may have formed, it does reveal that this galaxy has likely not evolved in the isolation previously assumed.
