Posted on by Ian O'Neill

Hubble Discovers a Strange Collection of White Dwarf… Dwarfs

Small helium white dwarfs can be caused by a binary partner (NASA)

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A collection of very odd white dwarfs have been discovered in a local globular cluster. Twenty-four white dwarfs (18 of them are new discoveries) have been spotted. Although these degenerate stars aren’t exactly an uncommon (they are the small sparkling remnants left over after star death), this particular set are unique; they are made from helium, rather than the “standard” carbon and oxygen. And they are small, even smaller than the smallest dwarfs.

How did this dense cluster of old stars evolve? It turns out their stellar material is being stolen, stifling their development…

“Helium-core white dwarfs have only about half the mass of typical white dwarfs, but they are found concentrated in the center of the cluster,” said Prof. Adrienne Cool, from San Francisco State University, in a paper to be published in the Astrophysical Journal in July. “With such low masses, the helium-core white dwarfs ought to be floating all around the cluster, according to theory. The fact that we find them only in the central regions suggests that they have heavy companions — partner stars that anchor them to the cluster center.”

The Hubble observations show 18 previously undiscovered helium-core white dwarfs (Jay Anderson / Space Telescope Science Institute)
The Hubble observations show 18 previously undiscovered helium-core white dwarfs (Jay Anderson / Space Telescope Science Institute)
Cool and co-author Rachel R. Strickler believe they are seeing a case of stellar plasma theft by companion binary stars in the NGC 6397 cluster, approximately 7,200 light years away. These binary partners not only anchor these strange-looking white dwarfs in the centre of the cluster, they also have a huge role to play during the dwarfs evolution.

Before a white dwarf emerges from a planetary nebula, the parent star will have gone through the red giant phase (a phase our Sun is expected to go through in 4-5 billion years time). If this red giant has a binary partner (which seems to be the case of the 24 white dwarfs in this study), the outer layers of the puffed-up giant will be stripped away by the partner, stifling the red giant’s evolution. As mass is lost, the giant never gets the chance to burn helium and then progressively heavier elements such as carbon and oxygen in and around its core. Helium then becomes the key component of these smaller-than-usual white dwarfs.

“This is the first time that helium-core white dwarf stars have been discovered in partnerships with other white dwarfs in a globular cluster,” Cool said. “This large sample allows us to answer questions about the mass and nature of the partner stars, and the prevalence of these kinds of binaries in the globular cluster.”

Binary stars are known to affect their partners fairly radically, they are even known to slow or even stop the development of black holes, stripping the outer layers of the dying star, stifling black hole development by removing mass from the parent star. However, not all questions have been answered.

From Cool’s calculations, 5% of the stars found in NGC 6397 should end their lives as dim helium-core white dwarf stars, but after studying Hubble data, many of these tiny dwarfs are missing. “It’s possible that these helium-core white dwarfs cool so slowly that they haven’t had time to get very faint yet,” Cool said.

There remains the possibility that the oldest binaries containing helium-core white dwarfs have actually been destroyed by interactions with other stars in the cluster. Regardless, this is a fascinating area of study. To understand how these ancient stars evolve will not only aid the development of globular cluster models, but it will provide an invaluable insight to how binary stars influence their partners.

Source: EurekAlert!

Posted on by Nancy Atkinson

NASA Will Try to Launch Hubble Repair Mission Early

STS-125 poster. Click for Hi-Res version.

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Personally, I think this move is just in response to the Onion’s most recent dig at NASA (“NASA Embarks on Epic Delay”) but mission managers for the upcoming Hubble repair mission are considering moving the launch of space shuttle Atlantis up one day to May 11. This would allow an extra day for launch attempts. May 12 had been the target day, but deputy program manager LeRoy Cain told reporters at a press conference on Thursday that the shuttle will likely be ready a day earlier, which would give Atlantis and extra day for a launch attempt before having to stand down for a week to allow the military to proceed with a previously scheduled launch at the Eastern Test Range. A decision about whether Atlantis will be ready to fly on the 11th will come next week Thursday (April 30) following a mission management review. But an accident at the launch pad that dinged one of Atlantis’ payload bay doors might hinder moving the launch up a day, and engineers are assessing if a repair is necessary.

A socket wrench at the launch pad. Credit: NASASpaceflight.com
A socket wrench at the launch pad. Credit: NASASpaceflight.com

A one-and-one-eighth-inch socket from a torque wrench fell from a service platform and hit Atlantis’ left payload bay door radiator while cargo for the Hubble repair mission was being installed. None of the cargo for the mission was damaged. Engineers will decide if any repairs are needed.

But moving the launch up a day may be a first for NASA.

“We prefer to have three launch attempts days available and the team is off evaluating May 11,” Cain said. “It looks very good, but it will be constrained by the work that needs to be done with the cargo elements. We’ll set the official launch date next week

If any delays occur (weather, technical, etc) that Atlantis can’t get off the pad by May 13, the next opportunity to launch wouldn’t be until May 22. NASA, the military and commercial operators share tracking, safety and other support services at Cape Canaveral Air Force Station. Usually, it takes at least two days to configure the range for supporting different types of rockets.

Members of the STS-125 crew at a press briefing. Credit: NASA
Members of the STS-125 crew at a press briefing. Credit: NASA

At a later press briefing yesterday, the crew of the STS-125 mission to Hubble said they are looking forward to the mission. “We are ready for this mission, we are trained and looking forward to executing everything we’ve been preparing for,” said the commander Scott Altman.

The other “big” news revealed (perhaps another first) during the crew press conference is that Mike Massimino, who has been Twittering during the training for the mission, (@Astro_Mike) will attempt to Twitter from space. Massimino said he wasn’t yet sure how the team would work out the technical issues, as space missions don’t usually have streaming internet.

“We’re going to be really busy so I’m not sure how much we’ll do this from orbit,” he said. “I’ll try to do it when I have free time in between missions. I can’t make any promises, but I’m going to try.”

Posted on by Anne Minard

Hubble Immortalizes Itself With New Image: “Fountain of Youth”


To commemorate the Hubble Space Telescope’s 19 years in space, the ESA and NASA have released an image of a celestial celebration. 

Two members in this trio of galaxies are apparently engaged in a gravitational tug-o-war, giving rise to a bright streamer of newborn blue stars that stretches 100,000 light years across.

 

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Constellation region near ARP 194. Credit: NASA, ESA Z. Levay and A. Fujii

Resembling a pair of owl’s eyes, the two nuclei of the colliding galaxies can be seen in the process of merging at the upper left. The bizarre blue bridge of material extending out from the northern component looks as if it connects to a third galaxy but in reality this galaxy is in the background, and not connected at all.

Hubble’s sharp view allows astronomers to try and sort out visually which are the foreground and background objects when galaxies, superficially, appear to overlap.

The blue “fountain” is the most striking feature of this galaxy troupe and it contains complexes of super star clusters that may have as many as dozens of individual young star clusters in them. It formed as a result of the interactions among the galaxies in the northern component of Arp 194. The gravitational forces involved in a galaxy interaction can enhance the star formation rate and give rise to brilliant bursts of star formation in merging systems.

The stream of material lies in front of the southern component of Arp 194, as shown by the dust that is silhouetted around the star cluster complexes.

The details of the interactions among the multiple galaxies that make up Arp 194 are complex. The system was most likely disrupted by a previous collision or close encounter. The shapes of all the galaxies involved have been distorted by their gravitational interactions with one another.

Arp 194, located in the constellation of Cepheus, resides approximately 600 million light-years away from Earth. Arp 194 is one of thousands of interacting and merging galaxies known in our nearby Universe.

The observations were taken in January 2009 with the Wide Field Planetary Camera 2. Blue, green and red filters were composited together to form the galaxy interaction image.

This picture was issued to celebrate the 19th anniversary of the launch of the Hubble Space Telescope aboard the space shuttle Discovery in 1990. In the past 19 years, Hubble has made more than 880,000 observations and snapped over 570,000 images of 29,000 celestial objects.

Image credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

Source: HubbleSite

Posted on by Nancy Atkinson

Incredible Light Show: Gas Jet Flaring From M87’s Black Hole

Hubble image of a gas jet blasing from the core of M87. Credit: NASA, ESA, and J. Madrid (McMaster University)

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Sometimes reality is stranger than fiction. The Hubble Space Telescope has been keeping an eye on the very active galaxy M87 for years, and has now captured a flare-up in a jet of matter blasting from the galaxy’s monster black hole. This 5,000-light-year-long, narrow beam of radiation and plasma is as bright as a Star Wars light saber and as destructive as the Death Star. This extragalactic jet is being fueled and ejected from the vicinity of a monster black hole that is 3 billion times the mass of our Sun. “I did not expect the jet in M87 or any other jet powered by accretion onto a black hole to increase in brightness in the way that this jet does,” says astronomer Juan Madrid of McMaster University in Hamilton, Ontario. “It grew 90 times brighter than normal. But the question is, does this happen to every single jet or active nucleus, or are we seeing some odd behavior from M87?”


The outburst is coming from a blob of matter, called HST-1, embedded in the jet, a powerful narrow beam of hot gas produced by the supermassive black hole residing in the core of this giant elliptical galaxy. HST-1 is so bright that it is outshining even M87’s brilliant core, whose monster black hole is one of the most massive yet discovered.

The glowing gas clump has taken astronomers on a rollercoaster ride of suspense. Astronomers watched HST-1 brighten steadily for several years, then fade, and then brighten again. They say it’s hard to predict what will happen next.

Hubble has been following the surprising activity for seven years, providing the most detailed ultraviolet-light view of the event. Other telescopes have been monitoring HST-1 in other wavelengths, including radio and X-rays. The Chandra X-ray Observatory was the first to report the brightening in 2000. HST-1 was first discovered and named by Hubble astronomers in 1999. The gas knot is 214 light-years from the galaxy’s core.

The flare-up may provide insights into the variability of black hole jets in distant galaxies, which are difficult to study because they are too far away. M87 is located 54 million light-years away in the Virgo Cluster, a region of the nearby universe with the highest density of galaxies.
Hubble gives astronomers a unique near-ultraviolet view of the flare that cannot be accomplished with ground-based telescopes. “Hubble’s sharp vision allows it to resolve HST-1 and separate it from the black hole,” Madrid explains.

Despite the many observations by Hubble and other telescopes, astronomers are not sure what is causing the brightening. One of the simplest explanations is that the jet is hitting a dust lane or gas cloud and then glows due to the collision. Another possibility is that the jet’s magnetic field lines are squeezed together, unleashing a large amount of energy. This phenomenon is similar to how solar flares develop on the Sun and is even a mechanism for creating Earth’s auroras.

The disk around a rapidly spinning black hole has magnetic field lines that entrap ionized gas falling toward the black hole. These particles, along with radiation, flow rapidly away from the black hole along the magnetic field lines. The rotational energy of the spinning accretion disk adds momentum to the outflowing jet.

Gas jet from M87. Credit: NASA, ESA, and J. Madrid (McMaster University)
Gas jet from M87. Credit: NASA, ESA, and J. Madrid (McMaster University)

Madrid assembled seven years’ worth of Hubble archival images of the jet to capture changes in the HST-1’s behavior over time. Some of the images came from observing programs that studied the galaxy, but not the jet.

He found data from the Space Telescope Imaging Spectrograph (STIS) that showed a noticeable brightening between 1999 and 2001. In images from 2002 to 2005, HST-1 continued to rise steadily in brightness. In 2003 the jet knot was more brilliant than M87’s luminous core. In May 2005 HST-1 became 90 times brighter than it was in 1999. After May 2005 the flare began to fade, but it intensified again in November 2006. This second outburst was fainter than the first one.

“By watching the outburst over several years, I was able to follow the brightness and see the evolution of the flare over time,” Madrid says. “We are lucky to have telescopes like Hubble and Chandra, because without them we would see the increase in brightness in the core of M87, but we would not know where it was coming from.”

Madrid hopes that future observations of HST-1 will reveal the cause of the mysterious activity. “We hope the observations will yield some theories that will give us some good explanations as to the mechanism that is causing the flaring,” Madrid says. “Astronomers would like to know if this is an intrinsic instability of the jet when it plows its way out of the galaxy, or if it is something else.”

The study’s results are published in the April 2009 issue of the Astronomical Journal.

Source: HubbleSite

Posted on by Anne Minard

Interview with Astronaut Mike Massimino on the Hubble Servicing Mission, Viewing Earth from Space and … Twitter?

The long-awaited final Hubble servicing mission is a month out now, and the crew of seven astronauts who have been in limbo since at least October are finally gearing up to go. The space shuttle Atlantis is set to launch from NASA’s Kennedy Space Center in Florida on May 12.

This will be the second Hubble mission for Astronaut Mike Massimino, and he’s been sharing his excitement about the mission via live interviews from NASA’s Johnson Space Flight Center and Twitter, a popular social networking site. We took advantage of the chance to ask Massimino some questions.

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Astronaut Mike Massimino suits up for spacewalk practice in the pool. Credit: NASA

So the final Hubble servicing mission is finally going to happen. How are you feeling about it? 

I’m feeling great. I’m ready, I think my crew’s ready, and looking forward to going into space and seeing Hubble again and seeing the Earth from space.  

On Twitter, you “tweeted” a few days ago: “viewing the Earth from space is the most beautiful site, words cannot describe the experience, can’t wait to see that sight again!” And it made me wonder how long you’ve wanted to have that perspective, and whether you dreamed of this sort of thing as a kid?

I dreamt about being an astronaut when I was a little kid. I was 6 years old when Neil Armstrong first walked on the moon.  But the view of the Earth … it is just so awesome to see the Earth from space. There’s no way to really prepare you for it; we can practice our space walks in the neutral buoyancy lab, we can go to simulators, but  there’s nothing that can prepare you for what your eyes will actually see when it comes to the beauty of space and the beauty of the Earth. I can’t really describe it with words, but I can describe what my thoughts were. When I really had the chance to look, while I was spacewalking, the first thought that went through my mind was “if you were in Heaven, this is what you would see.” And then the thought that replaced it was “no, no, it’s more beautiful than that. This is what Heaven must look like.”

You performed two spacewalks to service the telescope during the STS-109 mission in 2002. Since then you’ve worked in Mission Control and taught some classes. Why so long between missions? 

I flew in 2002, then I was hoping to get reassigned to another shuttle flight at some point, but the Columbia accident occurred. In the three years following Columbia, we didn’t have very many flights. I got assigned soon after STS 121 to the Hubble Space Telescope flight. Then comes that saga. My crew and I were assigned around Halloween, October 2006 … We thought we might be flying about a year and a half later. We were two weeks from launching in October of last year, and then we got delayed because something broke on the telescope. It’s been good for job security I guess. It gives you more time to get ready, and they hang onto you a little bit longer. 

Have you noticed any differences between preparing for this mission and preparing for the STS-109 flight?

STS-109 was my first flight. I was trying to figure out what I was going to do not to get in everybody’s way. I was wondering how I would react to space; I was kind of concerned about how I was going to do. This flight here, I’m pretty confident about how I’ll do … and I’m concerned a little bit more about how the team will do. It’s … a little more responsibility. I’m the experienced guy on our spacewalking team now. Actually it’s a little bit more enjoyable because I know what I’m going to do and I’m looking forward to it.

You’re on Twitter! Why? 

I feel very fortunate to have the opportunity to be an astronaut. I think I’m extremely lucky. We get to do so many wonderful things; one of my interests has been to try to share that with people the best I can. It seemed like this Twitter idea was a great way to share our experiences with other people. One of the great things about Twitter it doesn’t really take that long. You have 140 characters … I checked this weekend and we were up to 35,000 people–

You’re up to 40,000 now

… I figure if there are that many people listening, that’s a pretty good deal. You get responses to it. It’s just wonderful to hear the excitement and all the good wishes from people around the world. 

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The May servicing mission will be the fourth and final trip to the Hubble Space Telescope. Over the course of five spacewalks, astronauts will install two new instruments, repair two inactive instruments and replace parts that will keep the telescope functioning at least into 2014.

Check out Mike Massimino’s Twitter profile here, where he’ll continue tweeting about mission preparations. More information about the servicing mission is here, and more information about the Atlantis crew is here.