Posted on by Nancy Atkinson

Hubble Captures Surprisingly Restless Stars on the Move

NGC 3603 and its massive compact central star cluster was taken with the Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope. The region that was studied in detail to detect the motion of stars within the cluster is shown as a box. Credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

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Using the Hubble Space Telescope, astronomers from the Max Planck Institute for Astronomy made two observations ten years apart of the giant nebula NGC 3603 and found a surprising amount of movement and unrest in one of the most massive young star clusters in the Milky Way. The comparison images reveal several hundred stars continued to move for about 1 million years after the star cluster’s formation, with stellar motion not having “settled down” as expected. This new finding is at odds with current models of how such clusters evolve, and may force astronomers to rethink how star clusters form and develop.

While ordinary star clusters disperse over time as the different stars go their own separate ways, it was thought that very massive and compact clusters were different, and that they formed massive aggregations of stars known as globular clusters, whose tightly-packed stars remain gravitationally bound to each other for billions of years.

Conventional thinking was that stars with lower mass should move faster, and those with higher mass should move more slowly. But a team led by Wolfgang Brander, making high precision observations, found the stars in NGC 3603 are still moving at rates that are independent of their mass.

They found that all of the stars move at about the same average speed of 4.5 km/s (corresponding to a change in apparent position of a mere 140 micro-arc seconds per year). The average speed does not appear to vary with mass at all.

The team observed more than 800 stars and were able to obtain sufficiently precise speed measurements for 234 cluster stars of different masses and surface temperatures.

Partial view of the giant nebula (HII region) NGC 3603 with its central, 1 million year old compact starburst cluster. False-color image based on observations with the Wide Field/Planetary Camera 2 of the Hubble Space Telescope. The dominant green color signalizes light emitted as ionized hydrogen regains its missing electron ('recombination line H-alpha'). The field of view is about 160 arc seconds on each side. The image shape is due to the detector placement of the Wide Field/Planetary Camera. Credit: NASA/ESA/Wolfgang Brandner (MPIA), Boyke Rochau (MPIA) and Andrea Stolte (University of Cologne)

“Once our analysis was completed, we reached a precision of 27 millionths of an arc second per year,” said Boyke Rochau, the paper’s lead author. “Imagine you are in Bremen, observing an object that is located in Vienna. Now the object moves sideways by the breadth of a human hair. That’s a change in apparent position of about 27 millionths of an arc second.”

Apparently – and surprisingly – this very massive star cluster has not yet settled down. Instead, the stars’ velocities still reflect conditions from the time the cluster was formed, approximately one million years ago.

“For the first time, we have been able to measure precise stellar motions in such a compact young star cluster. This is key information for astronomers trying to understand how such clusters are formed, and how they evolve,” said team member Andrea Stolte from the University of Cologne.

Vexingly, the question of whether or not the massive young cluster in NGC 3603 will become a globular cluster remains open. Given the new results, it all depends on the speeds of the low-mass stars, which were too faint to allow for precise speed measurements with the Hubble Space Telescope. “To find out whether or not our star cluster will disperse, we will need to wait for the next generation of telescopes, such as the James Webb Space Telescope (JWST) or ESO’s European Extremely Large Telescope (E-ELT),” said Brandner.

The results have been published in the Letters section of the Astrophysical Journal. Read the paper here.

Sources: Max Planck Institute for Astronomy, Hubble ESA

Posted on by Nancy Atkinson

Scientist Explains New LOFAR Image of Quasar 3C196

Radio images of the quasar 3C 196 at 4 - 10 m wavelength (30 - 80 MHz frequency). Left: Data from LOFAR stations in the Netherlands only. The resolution is not sufficient to identify any substructure. Right: Blow-up produced with data from the German stations included. The resolution of this image is about ten times better and allows for the first time to distinguish fine details in this wavelength range. The colours are chosen to resemble what the human eye would see if it were sensitive to radiation at a wavelength ten million times larger than visible light. Image: Olaf Wucknitz, Bonn University (Click to enlarge image).

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We received several questions about our article on the new high-resolution LOFAR (LOw Frequency Array) image of quasar 3C196, concerning what was actually visible in this new image. We contacted LOFAR scientist Olaf Wucknitz from the Argelander-Institute for Astronomy at Bonn University in Germany, and he has provided an extensive explanation.

“3C196 is a quasar, the core of which is sitting right in the middle of the radio component,” Wucknitz said. “The core itself is not seen in radio observations but only on optical images. A possible reason for not seeing the core or the jets is that the central engine may not be very active at the moment (or rather it was not very active when the radiation left the object about 7 billion years ago). Alternatively it is possible that the inner parts of this source radiate very inefficiently so that we just do not see them in the radio images.”

In any case, he said, there must have been considerable activity earlier, because extensions of the jets that form radio lobes and hot spots are able to be seen in the image.

“The main lobes seem to be the bright SW component and the more compact NE component. When compared to observations at higher frequencies, these have the flattest spectra, i.e. they dominate at higher frequencies,” Wucknitz continued. “Then there is the other pair of components, the fuzzier E and W components. They are much weaker at higher frequencies.”

“The standard explanation for this would be that the jets from the core are changing its orientation with time (e.g. due to precession caused by a second black hole near the core, but this is very speculative). In this scenario the more extended components are older. Because of their age, the electrons causing the radiation have lost so much energy that we now see more low-frequency (i.e. low energy) radiation. The more compact components would be younger and therefore produce more high-frequency radiation.”

Interestingly, the W and E components show very different “colors” between 30-80 MHz, he said, so there must be some difference in the physical conditions in these two regions.

“Another possible explanation is that the compact components are the main lobes. There the jets interact with the surrounding medium. The matter is deflected and causes an outflow which we see as the other components.”

So basically, Wucknitz said, with the study of the data now available, they cannot draw firm conclusions, and he and his team have not had the opportunity to write a paper on the new image. “At the moment we are concentrating on getting LOFAR to run routinely and try to resist the temptation to do too much science with the first images. I hope that we can provide a real scientific analysis of this and similar images later this year.”

However, he suggested a couple of earlier papers that discuss quasar 3C196.

“Rotationally symmetric structure in two extragalactic radio sources” by Lonsdale, C. J.; Morison, I. describes the model of rotating jets for several obects including 3C196.

And this paper, Kiloparsec scale structure in the hotspots of 3C 196 by Lonsdale, C. J. discuses how previous observations by the MERLIN array revealed the presence of complex structure in each of the two bright hot spots in the quasar.

Wucknitz said he looks forward to delving into this object deeper as more of the LOFAR stations come online. “Once we can calibrate our new data better and produce slightly nicer images, we can hopefully say more and decide for one of the models,” he said.

Thanks to Olaf Wucknitz for providing an explanation of this new LOFAR image. Still have questions? Post them in the comments below.

Posted on by Nancy Atkinson

Voyager 2 Update from Dr. Ed Stone

Artist impression of Voyager. Image credit: NASA/JPL

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In early May 2010, the 33-year-old Voyager 2 spacecraft experienced an anomaly where the data it returned to Earth was unreadable. Engineers diagnosed the problem as a flip of a bit in the memory in the flight data system computer that packages data to transmit back to Earth, and were able to successfully reset the computer. On May 23, Voyager 2 sent back data that was again formatted properly, but the teams wanted to check out all the systems on the spacecraft to make sure everything was working properly. We checked in with Dr. Ed Stone, former director of JPL and the project scientist for the Voyager project since 1972 to get the latest news on how Voyager 2’s checkout is progressing.

“The science teams have confirmed that Voyager 2 is again transmitting science data in the expected format and the instruments are fully functional,” Stone said via email. “The only remaining action is to reset the clock in the spacecraft’s data system that lost time while the memory bit was in the wrong state. The reset commands will be sent to the Voyager 2 in the next two weeks.”

The flipped or bad bit in the flight data system was likely caused by a cosmic ray that slipped by the radiation protection on the spacecraft. Since the computer stores information in ones and zeroes, a cosmic ray hit can change the value of a memory bit. The concern was that the flipped bit took place in an important location that could have a serious effect on the spacecraft, but fortunately, the problem was solved “easily.”

I say easily in quotes because of the complexities of diagnosing and fixing a spacecraft at such great distances. Since Voyager 2 is about 13.8 billion kilometers, or 8.6 billion miles, from Earth, it takes nearly 13 hours for signals to reach the spacecraft and nearly 13 hours for signals to come down to NASA’s Deep Space Network on Earth.

Hats off to the scientists and engineers at JPL for their efforts and dedication so we all can continue to follow Voyager’s continuing journey to interstellar space.

Sources: JPL, email exchange with Dr. Ed Stone, Planetary Blog.

Posted on by Nancy Atkinson

Space Station Twitter Crew Returns Home

The Expedition 23 crew from the International Space Station landed safely in their Soyuz-17 spacecraft, concluding their five-and-a-half-month stay in space. Commander Oleg Kotov and Flight Engineers T.J. Creamer and Soichi Noguchi were welcomed by sunshine on Wednesday morning in Kazakhstan (11:25 pm EDT Tuesday). This crew may well be remembered as the ‘Twitter Crew’: Creamer posted the first “live” Tweet from space on Twitter from the now functioning internet on the ISS, which he helped to get up and running. Noguchi’s use of Twitter to post hundreds of images from space documented and shared his experiences in space like no previous astronaut, as he garnered over 250,000 Twitter “followers,” and his images were featured on many blogs and news sites.
Continue reading “Space Station Twitter Crew Returns Home”

Posted on by Fraser Cain

What is the Center of the Earth Made Of?

The Earths interior (University of Chicago)

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We know the surface of the Earth is made of rock, we can examine it ourselves. But what is the center of the Earth made of? Well, reach into your pockets and pull out some coins. That’s roughly what the center of the Earth is made of.

The Earth is broken up into layers. The outermost layer is the crust- that’s what you’re standing on. About 30 km below your feet is where the next layer of the Earth, the mantle, starts. The mantle makes up the majority of the interior of the Earth, and its composed of heated rock under high pressure. But inside the mantle is the core of the Earth, and it’s made of metal.

The Earth’s core is broken up into two distinct regions. The inner core is a sphere of solid metal that measures about 2,440 km across. It’s believed to be comprised of 80% iron and 20% nickel. Surrounding this solid inner core is an outer core of liquid metal that extends for approximately another 2,000 km. Geologists believe that the movement of metal in the outer core gives the Earth its magnetic field, allowing compasses to work.

Needless to say, the center of the Earth is incredibly hot. Scientists estimate that the core of the Earth could get as hot as 7,000 kelvin, and about 5,700 kelvin at the border between the inner and outer cores.

We’ve written many articles about the core of the Earth. Here’s an article about how far down the center of the Earth is, and here’s an article about the center of the Earth.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Posted on by Fraser Cain

VY Canis Majoris Supernova

VY Canis Majoris. The biggest known star.
Size comparison between the Sun and VY Canis Majoris, which once held the title of the largest known star in the Universe. Credit: Wikipedia Commons/Oona Räisänen

VY Canis Majoris is a red giant star located in the constellation Canis Major. Measuring between 1800-2100 times the size of the Sun, astronomers think that this star is at the end of its life, and will explode as a supernova in the relatively near future. So, what would a VY Canis Majoris supernova look like?

Astronomers classify VY Canis Majoris as a red hypergiant star – it’s thought to have 15-25 times the mass of the Sun. During the main sequence phase of its life, it probably had upwards of 40 times the mass of the Sun, but it has been blowing much of its material into space with its powerful stellar winds. It has a surface temperature of 3,000 kelvin, which is relatively cool for a star.

VY Canis Majoris is at the end of its life. It lived a short life in the main sequence phase of its life, and then ballooned up as a red hypergiant. It will remain in this phase for a few hundred thousand years. Exactly how long the star will last isn’t known, but it doesn’t have millions of years left.

Once it finally runs out of fuel in its core, the star will collapse down and become a core-collapse supernova. This is where the central regions of the star become a neutron star or black hole, and the outer regions are ejected into space. For a few days or weeks, the wreckage of the explosion will outshine the rest of the galaxy, and be easily visible from here on Earth.

Don’t worry, we’re not in any danger. VY Canis Majoris is located 5,000 light-years from Earth; all we’ll get to see is a pretty light show when the star finally explodes.

We’ve written several articles about VY Canis Majoris for Universe Today. Here’s an article that explains why it’s the biggest star, and here’s an article about the star itself.

If you’d like more information on VY Canis Majoris Supernova, check out Hubblesite’s News Releases on Supernova, and here’s a link to the NASA Science Homepage: Supernova for recent stories and images.

We’ve done many episodes of Astronomy Cast about stars. Listen here, Episode 12: Where Do Baby Stars Come From?

Posted on by Nancy Atkinson

Menagerie of Celestial Objects in New Image of the Large Magellanic Cloud

A new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile reveals a celestial menagerie of different objects and phenomena in part of the Large Magellanic Cloud. The field of view is about one degree across. Credit: ESO

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From an ESO press release:

Astronomers often turn their telescopes to the Large Magellanic Cloud (LMC), one of the closest galaxies to our own Milky Way, in their quest to understand the Universe. In this spectacular new image from the Wide Field Imager (WFI) at ESO’s La Silla Observatory in Chile, a celestial menagerie of different objects and phenomena in part of the LMC is on display, ranging from vast globular clusters to the remains left by brilliant supernovae explosions. This fascinating observation provides data for a wide variety of research projects unravelling the life and death of stars and the evolution of galaxies.

The LMC is only about 160,000 light-years from our own Milky Way — very close on a cosmic scale. This proximity makes it a very important target as it can be studied in far more detail than more distant systems. The LMC lies in the constellation of Dorado (the Swordfish), deep in the southern sky and well placed for observations from ESO’s observatories in Chile. It is one of the galaxies forming the Local Group surrounding the Milky Way. Though enormous on a human scale, the LMC is less than one tenth the mass of our home galaxy and spans just 14,000 light-years compared to about 100,000 light-years for the Milky Way.

Astronomers refer to it as an irregular dwarf galaxy. Its irregularity, combined with its prominent central bar of stars suggests to astronomers that tidal interactions with the Milky Way and fellow Local Group galaxy, the Small Magellanic Cloud, could have distorted its shape from a classic barred spiral into its modern, more chaotic form.

This spectacular new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile reveals a celestial menagerie of different objects and phenomena in part of the Large Magellanic Cloud, a small companion galaxy to our own Milky Way. Many clusters are visible including an unusually young globular cluster and the remains of a brilliant supernovae explosion. A selection of objects are labeled and shown as enlarged cutouts. Credit: ESO

This image is a mosaic of four pictures from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. The image covers a region of sky more than four times as large as the full Moon. The huge field of view of this camera makes it possible to see a very wide range of objects in the LMC in a single picture, although only a small part of the entire galaxy can be included. Dozens of clusters of young stars can be seen as well as traces of glowing gas clouds. Huge numbers of faint stars fill the image from edge to edge and in the background, more galaxies, far beyond the LMC, are visible.

Globular clusters are collections of hundreds of thousands to millions of stars bound by gravity into a roughly spherical shape just a few light-years across. Many clusters orbit the Milky Way and most are ancient, over ten billion years old, and composed mainly of old red stars. The LMC also has globular clusters and one is visible as the fuzzy white oval cluster of stars in the upper right part of the image. This is NGC 1978, an unusually massive globular cluster. Unlike most other globular clusters, NGC 1978 is believed to be just 3.5 billion years old. The presence of this kind of object in the LMC leads astronomers to think that the LMC has a more recent history of active star formation than our own Milky Way.

As well as being a vigorous region of star birth, the LMC has also seen many spectacular stellar deaths in the form of brilliant supernova explosions. At the top right of the image, the remnant of one such supernova, a strangely shaped wispy cloud called DEM L 190, often also referred to as N 49, can be seen. This giant cloud of glowing gas is the brightest supernova remnant in the LMC, and is about 30 light-years across. At the centre, where the star once burned, now lies a magnetar, a neutron star with an extremely powerful magnetic field. It was only in 1979 that satellites orbiting Earth detected a powerful gamma-ray burst from this object, drawing attention to the extreme properties of this new class of stellar exotica created by supernova explosions.

This part of the Large Magellanic Cloud is so packed with star clusters and other objects that astronomers can spend entire careers exploring it.

Posted on by Nancy Atkinson

Retro Black Holes Are More Powerful

This artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets of radio waves.Image credit: NASA/JPL-Caltech

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Black holes seem to defy our comprehension and be contrary to conventional understanding. So perhaps it is not entirely surprising to find that supermassive black holes which have a retrograde or backwards spin might be more powerful and produce more ferocious jets of gas. While this new finding goes against what astronomers had thought for decades, it also helps solve a mystery why some black holes have no jets at all.

Powerful jets stream out from the accretion disks that spin around many supermassive black holes. The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow – the retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this “spin paradigm” model. For example, some prograde black holes had been found with no jets.

Theoretical astrophysicist David Garofalo and his colleagues have been studying the motion of black holes for years, and in previous papers, they proposed that the backward, or retrograde, black holes spew the most powerful jets, while the prograde black holes have weaker or no jets.

Their new study links their theory with observations of galaxies across time, or at varying distances from Earth. They looked at both “radio-loud” galaxies with jets, and “radio-quiet” ones with weak or no jets. The term “radio” comes from the fact that these particular jets shoot out beams of light mostly in the form of radio waves.

The results showed that more distant radio-loud galaxies are powered by retrograde black holes, while relatively closer radio-quiet objects have prograde black holes. According to the team, the supermassive black holes evolve over time from a retrograde to a prograde state.

“This new model also solves a paradox in the old spin paradigm,” said David Meier, a theoretical astrophysicist at JPL not involved in the study. “Everything now fits nicely into place.”

The scientists say that the backward black holes shoot more powerful jets because there’s more space between the black hole and the inner edge of the orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold’s conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

“If you picture yourself trying to get closer to a fan, you can imagine that moving in the same rotational direction as the fan would make things easier,” said Garofalo. “The same principle applies to these black holes. The material orbiting around them in a disk will get closer to the ones that are spinning in the same direction versus the ones spinning the opposite way.”

Jets and winds play key roles in shaping the fate of galaxies. Some research shows that jets can slow and even prevent the formation of stars not just in a host galaxy itself, but also in other nearby galaxies.

“Jets transport huge amounts of energy to the outskirts of galaxies, displace large volumes of the intergalactic gas, and act as feedback agents between the galaxy’s very center and the large-scale environment,” said team member Rita M. Sambruna, from Goddard Space Flight Center. “Understanding their origin is of paramount interest in modern astrophysics.”

The team’s paper was published in the May 27 Monthly Notices of the Royal Astronomical Society.

Source: JPL

Posted on by Jerry Coffey

Is Mars Bigger Than Earth?

Mars Compared to Earth. Image credit: NASA/JPL

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Occasionally, a reader asks ”is Mars bigger than Earth?”. No, Mars is about one half of the size of Earth. Below is a comparison chart so the you can get an idea of how much smaller Mars is than Earth

Earth Mars
Diameter 12,742 km 6,792 km
Surface Area 510,072,000 km2 144,798,500km2
Volume 1.08321×1012km3 1.6318×1011km3
Mass 5.9736×1024kg 6.4185×1023kg

The diameter of Mars is about 53% of Earth’s and the surface area is close to 38% of Earth’s. When you put the numbers into a percentage, the surface area really seems small, but it is equal to all of the dry land on Earth. Scientists have found evidence of ancient liquid water on Mars. That means there were rivers and, possibly, oceans on the Red Planet. Imagine how small the available living space would have been then. Couple that with Mars having several of the tallest mountains and the deepest canyon in the Solar System and you realize exactly how little usable surface there really is on the planet.

Mars is the number one planet that scientists will mention when they are talking about terraforming. Transforming Mars would take centuries. Christopher McKay of NASA Ames Research Center believes that the key steps would be, first, releasing greenhouse gases to thicken the Martian atmosphere. This will help the planet retain heat from the Sun while filtering its radiation. The increased temperature would vaporize some of the carbon dioxide trapped in and on the planet’s surface. The CO2 will increase the greenhouse effect, warming the planet even more. The temperature could increase by as much as 70 degrees on the Celsius scale. The increased temperature will melt the subsurface water ice on Mars, creating rain, rivers, and lakes. The water vapor from this release would also increase the atmospheric pressure to a level equivalent to what is seen at high elevations here on Earth. After all of these steps, the air would still be 90% carbon dioxide or higher. This is when plant life would be introduced to convert some of that carbon dioxide into oxygen. While humans could occupy the planet as the plants are being introduced, it would be several centuries before they would be able to remove their oxygen masks.

The answer to ”is Mars bigger than Earth” is no. The planet may be minute compared to Earth, but it is seen as a world full of potential by scientists. It is the most studied planet other than Earth, so be sure to look around for more information on the Red Planet.

We’ve written many articles about Mars for Universe Today. Here’s an article with some interesting facts about Mars, and here’s the distance from Earth to Mars.

If you’d like more info on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We’ve also recorded an episode of Astronomy Cast all about Mars. Listen here, Episode 52: Mars.

Sources:
http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
http://quest.nasa.gov/mars/background/terra2.html