Posted on by Jean Tate

Better Late Than Never: Dwarf Galaxies Finally Come Together

Hickson 31 (Credit: NASA, ESA, and S. Gallagher (The University of Western Ontario), and J. English (University of Manitoba))

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Have you heard of ‘living fossils’? The coelacanth, the ginko tree, the platypus, and several others are species alive today which seem to be the same as those found as fossils, in rocks up to hundreds of millions of years old.

Now combined results from the Hubble Space Telescope, Spitzer, Galaxy Evolution Explorer (GALEX), and Swift show that there are ‘living galaxy fossils’ in our own backyard!

Hubble: red, yellow-green, and blue; Spitzer: orange; GALEX: purple

Hickson Compact Group 31 is one of 100 compact galaxy groups catalogued by Canadian astronomer Paul Hickson; the recent study of them – led by Sarah Gallagher of The University of Western Ontario in London, Ontario – shows that the four dwarf galaxies in it are in the process of coming together (or ‘merging’ as astronomers say).

Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies are relatively nearby, only 166 million light-years away.

New images of this foursome by NASA’s Hubble Space Telescope offer a window into the universe’s formative years when the buildup of large galaxies from smaller building blocks was common.

Astronomers have known for decades that these dwarf galaxies are gravitationally tugging on each other. Their classical spiral shapes have been stretched like taffy, pulling out long streamers of gas and dust. The brightest object in the Hubble image is actually two colliding galaxies. The entire system is aglow with a firestorm of star birth, triggered when hydrogen gas is compressed by the close encounters between the galaxies and collapses to form stars.

The Hubble observations have added important clues to the story of this interacting group, allowing astronomers to determine when the encounter began and to predict a future merger.

“We found the oldest stars in a few ancient globular star clusters that date back to about 10 billion years ago. Therefore, we know the system has been around for a while,” says Gallagher; “most other dwarf galaxies like these interacted billions of years ago, but these galaxies are just coming together for the first time. This encounter has been going on for at most a few hundred million years, the blink of an eye in cosmic history. It is an extremely rare local example of what we think was a quite common event in the distant universe.”

In other words, a living fossil.

Everywhere the astronomers looked in this group they found batches of infant star clusters and regions brimming with star birth. The entire system is rich in hydrogen gas, the stuff of which stars are made. Gallagher and her team used Hubble’s Advanced Camera for Surveys to resolve the youngest and brightest of those clusters, which allowed them to calculate the clusters’ ages, trace the star-formation history, and determine that the galaxies are undergoing the final stages of galaxy assembly.

The analysis was bolstered by infrared data from NASA’s Spitzer Space Telescope and ultraviolet observations from the Galaxy Evolution Explorer (GALEX) and NASA’s Swift satellite. Those data helped the astronomers measure the total amount of star formation in the system. “Hubble has the sharpness to resolve individual star clusters, which allowed us to age-date the clusters,” Gallagher adds.

Hubble reveals that the brightest clusters, hefty groups each holding at least 100,000 stars, are less than 10 million years old. The stars are feeding off of plenty of gas. A measurement of the gas content shows that very little has been used up – further proof that the “galactic fireworks” seen in the images are a recent event. The group has about five times as much hydrogen gas as our Milky Way Galaxy.

“This is a clear example of a group of galaxies on their way toward a merger because there is so much gas that is going to mix everything up,” Gallagher says. “The galaxies are relatively small, comparable in size to the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Their velocities, measured from previous studies, show that they are moving very slowly relative to each other, just 134,000 miles an hour (60 kilometers a second). So it’s hard to imagine how this system wouldn’t wind up as a single elliptical galaxy in another billion years.”

Adds team member Pat Durrell of Youngstown State University: “The four small galaxies are extremely close together, within 75,000 light-years of each other – we could fit them all within our Milky Way.”

Why did the galaxies wait so long to interact? Perhaps, says Gallagher, because the system resides in a lower-density region of the universe, the equivalent of a rural village. Getting together took billions of years longer than it did for galaxies in denser areas.

Source: HubbleSite News Release. Gallagher et al.’s results appear in the February issue of The Astronomical Journal (the preprint is arXiv:1002.3323)

Posted on by Nancy Atkinson

Hubble Captures Double Aurorae Light Show on Saturn

Hubble's view of Saturn with a double view of its fluttering aurorae. Credit: NASA, ESA and Jonathan Nichols (University of Leicester)


In January and March 2009, researchers using Hubble took advantage of a rare opportunity to record Saturn when its rings are edge-on, resulting in a unique look featuring both of the giant planet’s poles. And Saturn cooperated by providing an incredible double light show with Saturn’s own northern and southern lights. Since Saturn is only in this position every 15 years or so, this favorable orientation has allowed a sustained study of the two beautiful and dynamic aurorae.

Since it takes Saturn almost thirty years to orbit the Sun, the opportunity to image both of its poles occurs only twice in that period. Hubble has been snapping pictures of the planet at different angles since the beginning of the mission in 1990, but 2009 brought a unique chance for Hubble to image Saturn with the rings edge-on and both poles in view. At the same time Saturn was approaching its equinox so both poles were equally illuminated by the Sun’s rays.

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These recent observations go well beyond just a still image and have allowed researchers to monitor the behavior of both Saturn’s poles in the same shot over a sustained period of time. The movie they created from the data, collected over several days during January and March 2009, has aided astronomers studying both Saturn’s northern and southern aurorae. Given the rarity of such an event, this new footage will likely be the last and best equinox movie that Hubble captures of our planetary neighbor.

Despite its remoteness, the Sun’s influence is still felt by Saturn. The Sun constantly emits particles that reach all the planets of the Solar System as the solar wind. When this electrically charged stream gets close to a planet with a magnetic field, like Saturn or the Earth, the field traps the particles, bouncing them back and forth between its two poles. A natural consequence of the shape of the planet’s magnetic field, a series of invisible “traffic lanes” exist between the two poles along which the electrically charged particles are confined as they oscillate between the poles. The magnetic field is stronger at the poles and the particles tend to concentrate there, where they interact with atoms in the upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of the Earth’s polar regions know as the northern and southern lights.

At first glance the light show of Saturn’s aurorae appears symmetric at the two poles. However, analysing the new data in greater detail, astronomers have discovered some subtle differences between the northern and southern aurorae, which reveal important information about Saturn’s magnetic field. The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn’s magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south. As a result, the electrically charged particles in the north are accelerated to higher energies as they are fired toward the atmosphere than those in the south. This confirms a previous result obtained by the space probe Cassini, in orbit around the ringed planet since 2004.

Source: ESA

Posted on by Nancy Atkinson

New Hubble Images Show Pluto is Changing

New images of Pluto from the Hubble Space Telescope. Credit: NASA, ESA, and M. Buie (Southwest Research Institute).

Pluto-philes (and astronomers, too) have always bemoaned the fact that the best image of the principal dwarf planet wase just a fuzzy, pixelized haze. Bemoan no more. The most detailed look to date of the entire surface of Pluto has been constructed from hundreds of images taken by the Hubble Space Telescope. The images were taken during 2002 to 2003, and it took four years of computer crunching and software tweaking to create the global images. Surprisingly, the images show Pluto changed noticeably during the two-year photo shoot; the dwarf planet’s color became “redder,” and astronomers could see Pluto’s ice sheets were shifting.

“These Hubble pictures represent a true-color appearance of what you would see if you were near Pluto, comparable to looking at our own Moon with the naked eye,” said principal investigator Marc Buie of the Southwest Research Institute. “We now know we’re looking at something that has the biggest surface changes of any object in our solar system.”

The pictures show nitrogen ice growing and shrinking, getting brighter in the north and darker in the south.

Buie and planet hunter Mike Brown from Caltech introduced the Hubble images during a teleconference with reporters today, and emphasized how surprised they were with the changes seen on Pluto in just a relatively short period of time. Even accounting for seasonal changes, seasons can last 120 years in some regions of Pluto.

The top picture was taken in 1994 by the European Space Agency’s Faint Object Camera. The bottom image was taken in 2002-2003 by the Advanced Camera for Surveys. The dark band at the bottom of each map is the region that was hidden from view at the time the data were taken. Credit: NASA, ESA, and M. Buie (Southwest Research Institute)

They said the images underscore that Pluto is not simply a ball of ice and rock but a dynamic world that undergoes dramatic atmospheric changes. While they believe the changes are driven by the seasons, it may mostly come from how quickly things can change on Pluto. The seasons are propelled as much by the planet’s 248-year elliptical orbit as its axial tilt — unlike Earth where the tilt alone drives seasons. On Pluto spring transitions to polar summer quickly in the northern hemisphere because Pluto is moving faster along its orbit when it is closer to the Sun.

“If Earth had such an extreme orbit, and we were experiencing a nice springtime day with 60-70 degree F temperatures, as the orbit changed it could suddenly drop to -90 degrees F,” said Brown.

There is also a mysterious bright spot on the center of Pluto, which has been observed in earlier images. But the spot is unusually rich in carbon monoxide frost.

Click here to see a video of Pluto rotating.

The astronomers said Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away. Buie said we won’t have a better look at Pluto until the New Horizon’s spacecraft is six months away from the dwarf planet in 2015.

The images were taken with the Advanced Camera for Surveys on HST, and the 348 images taken in 2002 and 2003 were the last ones taken of Pluto with high enough resolution to be useful. “I had time allocated two years ago to look at Pluto, which came just three or four weeks after the high resolution camera failed,” Buie. “That was very disappointing.”

But the images do show Pluto is significantly redder than it had been for the past several decades. Astronomers use the word “red” to mean it reflects more red light than blue or green light. To the human eye, Pluto has a yellowish-orange color, and is about 20% redder than it used to be. “It’s not as red as the surface of Mars, but more red than Io,” Buie said.

Red is usually associated with carbon. The astronomers said there is also methane, which is not usually stable in an environment like Pluto’s.

“This business about the color change had me scared for awhile,” Buie confessed. “I got the result years ago, but it was so hard to understand and believe. I’m still nervous about it. It could be that I completely screwed this up, but I can tell you Charon is on the same images, and Charon has the same color throughout but Pluto changed. I don’t’ know how the camera system on HST could have given me the wrong colors on Pluto.”

This was previously the best image of Pluto, taken in 2000 by HST. Credit: Eliot Young (SwRI) et al., NASA

Someone suggested that Pluto is reddening because of its recent demotion from full planethood. “Yes, people have said that Pluto is mad at me,” said Brown, who has the nickname of the “Pluto killer” because he discovered other Kuiper Belt objects which led to the new class of dwarf planets.

“For a long time Pluto was this lonely oddball that we didn’t have anything else to compare it with,” said Brown. “Understanding this all as a new class of objects is a much more interesting way of looking at the solar system and it is quite a bit of fun, too.”

More information from Buie’s webpage on the Pluto images.

The paper about the images isn’t posted online yet, but it will be up on this webpage soon.

Source: Conference call.
Additional images and info from NASA

Posted on by Nancy Atkinson

Double Hubble Sequence Shows Galaxies Go Spiral

This image created from data taken from both the NASA/ESA Hubble Space Telescope and the Sloan Digital Sky Survey demonstrates that the Hubble sequence six billion years ago was very different from the one that astronomers see today. Credit: NASA, ESA, Sloan Digital Sky Survey, R. Delgado-Serrano and F. Hammer (Observatoire de Paris)

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Galaxies come in all sorts of shapes. But in the past, the various galaxy shapes used to be more diverse and “peculiar” than they are now. Over time, according to a new study, galaxies tend to become spirals. “Six billion years ago, there were many more peculiar galaxies than now — a very surprising result,” said Rodney Delgado-Serrano, lead author of a new paper. “This means that in the last six billion years, these peculiar galaxies must have become normal spirals, giving us a more dramatic picture of the recent Universe than we had before.”

Using data from the Hubble Space Telescope and the Sloan Digital Sky Survey, a team of astronomers created the first demographic census of galaxy types at two different points in the Universe’s history, putting together two Hubble sequences from different eras that help explain how galaxies form. The results showed that the Hubble sequence six billion years ago was very different from the one that astronomers see today.

The top image represents the current — or local — universe, and the bottom image represents the make up of the distant galaxies (six billion years ago), showing a much larger fraction of peculiar galaxies. In sampling 116 local galaxies and 148 distant galaxies, the researchers found that more than half of the present-day spiral galaxies had so-called peculiar shapes only 6 billion years ago.

Edwin Hubble invented the Hubble Sequence, sometimes called the Hubble tuning-fork diagram. The diagram divides galaxies into three 3 broad classes based on their basic shapes: spiral, barred spiral, and elliptical.

“Our aim was to find a scenario that would connect the current picture of the Universe with the morphologies of distant, older galaxies — to find the right fit for this puzzling view of galaxy evolution,” said François Hammer of the Observatoire de Paris who led the team of astronomers.

The astronomers think that these peculiar galaxies did indeed become spirals through collisions and merging. This is contrary to the widely held opinion that galaxy mergers result in the formation of elliptical galaxies, but Hammer and his team propose a “spiral rebuilding” hypothesis, which suggests that peculiar galaxies affected by gas-rich mergers are slowly reborn as giant spirals with discs and central bulges.

Crashes between galaxies give rise to enormous new galaxies and, although it was commonly believed that galaxy mergers decreased significantly eight billion years ago, the new result implies that mergers were still occurring frequently after that time — up to as recently as four billion years ago.

Link to higher resolution version of the top image.

Papers:
Hammer, et al.
Delgado-Serrano et al.

Source: Space Telescope Institute

Posted on by Nancy Atkinson

Hubble Takes A Look at Possible Asteroid Collision

Hubble Views of Comet-like Asteroid P/2010 A2. Credit: NASA, ESA, and D. Jewitt (UCLA)

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We reported earlier that on January 6, 2010, ground-based observatories may have spotted evidence of an asteroid collision in the asteroid belt. Now, the Hubble Space Telescope has taken a look at the mysterious X-shaped debris pattern and trailing streamers of dust. With Hubble’s sharp vision, astronomers believe a head-on collision between two asteroids has actually occured. Astronomers have long thought the asteroid belt is being ground down through collisions, but such a smashup has never been seen before.

“This is quite different from the smooth dust envelopes of normal comets,” said principal investigator David Jewitt of the University of California at Los Angeles. “The filaments are made of dust and gravel, presumably recently thrown out of the nucleus. Some are swept back by radiation pressure from sunlight to create straight dust streaks. Embedded in the filaments are co-moving blobs of dust that likely originated from tiny unseen parent bodies.”

Asteroid collisions would likely have an average impact speed of more than 11,000 miles per hour, or five times faster than a rifle bullet. The comet-like object imaged by Hubble, called P/2010 A2, was first discovered by the Lincoln Near-Earth Asteroid Research, or LINEAR, program sky survey on Jan. 6. New Hubble images taken on Jan. 25 and 29 show a complex X-pattern of filamentary structures near the nucleus.
Hubble shows the main nucleus of P/2010 A2 lies outside its own halo of dust. This has never been seen before in a comet-like object. The nucleus is estimated to be 460 feet in diameter.

Close-up of Comet-like Asteroid P/2010 A2. Credit: NASA, ESA, and D. Jewitt (UCLA)

Normal comets fall into the inner regions of the solar system from icy reservoirs in the Kuiper Belt and Oort Cloud. As a comet nears the sun and warms up, ice near the surface vaporizes and ejects material from the solid comet nucleus via jets. But P/2010 A2 may have a different origin. It orbits in the warm, inner regions of the asteroid belt where its nearest neighbors are dry rocky bodies lacking volatile materials.

This leaves open the possibility that the complex debris tail is the result of an impact between two bodies, rather than ice simply melting from a parent body.

“If this interpretation is correct, two small and previously unknown asteroids recently collided, creating a shower of debris that is being swept back into a tail from the collision site by the pressure of sunlight,” Jewitt said.

The main nucleus of P/2010 A2 would be the surviving remnant of this so-called hypervelocity collision.

“The filamentary appearance of P/2010 A2 is different from anything seen in Hubble images of normal comets, consistent with the action of a different process,” Jewitt said. An impact origin also would be consistent with the absence of gas in spectra recorded using ground-based telescopes.

The asteroid belt contains abundant evidence of ancient collisions that have shattered precursor bodies into fragments. The orbit of P/2010 A2 is consistent with membership in the Flora asteroid family, produced by collisional shattering more than 100 million years ago. One fragment of that ancient smashup may have struck Earth 65 million years ago, triggering a mass extinction that wiped out the dinosaurs. But, until now, no such asteroid-asteroid collision has been caught “in the act.”

At the time of the Hubble observations, the object was approximately 180 million miles from the sun and 90 million miles from Earth. The Hubble images were recorded with the new Wide Field Camera 3 (WFC3).

Source: HubbleSite

Posted on by Nancy Atkinson

Latest from Hubble: Star Formation Fizzling Out in Nearby Galaxy

NGC 2976.. NASA, ESA, and J. Dalcanton and B. Williams (University of Washington, Seattle)

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Most galaxies are throughout the universe are happenin’ places, with all sorts of raucous star formation going on. But for a nearby, small spiral galaxy, the star-making party is almost over. In this latest Hubble release, astronomers were surprised to find that star-formation activities in the outer regions of NGC 2976 are fizzling out, and any celebrating is confined to a few die-hard partygoers huddled in the galaxy’s inner region.

The reason? Well, the star birth began when another party-crashing galaxy interacted with NGC 2976. But that happened long ago, and now star formation in the galaxy is fizzling out in the outer parts as some of the gas was stripped away and the rest collapsed toward the center. With no gas left to fuel the party, more and more regions of the galaxy are going to sleep.

“Astronomers thought that grazing encounters between galaxies can cause the funneling of gas into a galaxy’s core, but these Hubble observations provide the clearest view of this phenomenon,” explains astronomer Benjamin Williams of the University of Washington in Seattle, who directed the Hubble study, which is part of the ACS Nearby Galaxy Survey Treasury (ANGST) program. “We are catching this galaxy at a very interesting time. Another 500 million years and the party will be over.”

NGC 2976 does not look like a typical spiral galaxy. It has a star-forming disk, but no obvious spiral pattern. Its gas is centrally concentrated, but it does not have a central bulge of stars. The galaxy resides on the fringe of the M81 group of galaxies, located about 12 million light-years away in the constellation Ursa Major.

“The galaxy looks weird because an interaction with the M81 group about a billion years ago stripped some gas from the outer parts of the galaxy, forcing the rest of the gas to rush toward the galaxy’s center, where it is has little organized spiral structure,” Williams says.

The galaxy’s relatively close distance to Earth allowed Hubble’s Advanced Camera for Surveys (ACS) to resolve hundreds of thousands of individual stars. What look like grains of sand in the image are actually individual stars. Studying the individual stars allowed astronomers to determine their color and brightness, which provided information about when they formed.

The image was taken over a period in late 2006 and early 2007.

“This type of observation is unique to Hubble,” Williams says. “If we had not been able to pick out individual stars, we would have known that the galaxy is weird, but we would not have dug up evidence for a significant gas rearrangement in the galaxy, which caused the stellar birth zone to shrink toward the galaxy’s center.”

Simulations predict that the same “gas-funneling” mechanism may trigger starbursts in the central regions of other dwarf galaxies that interact with larger neighbors. The trick to studying the effects of this process in detail, Williams says, is being able to resolve many individual stars in galaxies to create an accurate picture of their evolution.

Williams’ results will appear in the January 20, 2010 issue of The Astrophysical Journal.

Source: HubbleSite

Posted on by Nancy Atkinson

Hubble Repairman to Lead Space Telescope Science Institute

John Grunsfeld. Credit: NASA

Self proclaimed “Hubble Hugger” and telescope repairman Dr. John Grunsfeld has been appointed Deputy Director of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, the organization that coordinates all the science done with HST. Grunsfeld’s new job starts today, January 4, 2010. “This is an incredibly exciting opportunity for me to work at a focal point of top astronomers at the leading edge of scientific inquiry. The team at STScI has a demonstrated record of meeting the high performance challenges of operating the Hubble Space Telescope, and preparing for the James Webb Space Telescope. I look forward to working with this excellent team as we continue to explore the mysteries of the universe.”

Grunsfeld is a veteran of five space flights, including three missions to service HST: STS-103 in Dec. 1999, STS-109 in March 2002, and STS-125 in May 2009. He has logged over 835 hours in space, including nearly 60 hours of Extravehicular Activity during eight space walks.

He succeeds Dr. Michael Hauser, who stepped down in October. STScI is the science operations center for NASA’s orbiting Hubble Space Telescope and the James Webb Space Telescope planned to be launched in 2014.

Grunsfeld’s research has covered X-ray and gamma-ray astronomy, high-energy cosmic ray studies, and development of new detectors and instrumentation. Grunsfeld has conducted observations of the far-ultraviolet spectra of faint astronomical objects and the polarization of ultraviolet light coming from stars and distant galaxies.

“We are absolutely delighted that he has accepted the position,” said STScI Director, Dr. Matt Mountain. “John brings to us a wealth of expertise in the areas of space exploration concepts and technologies for use beyond low-earth orbit. He will be invaluable in our continued efforts to conduct world-class science with state-of-the-art observatories and instrumentation.

Source: HubbleSite, STSci

Posted on by Nancy Atkinson

Blue Stragglers Can Be Either Vampires or Stellar Bad-Boys

Messier 30, from HST’s Advanced Camera for Surveys. Credit: NASA, ESA and Francesco Ferraro (University of Bologna

Blue stragglers are stars that stay on the main sequence longer than expected. They even appear to regress from “old age” back to a hotter and brighter “youth,” gaining a new lease on life in the process. Astronomers have thought blue stragglers were “vampires” that suck fresh hydrogen from companion stars to heat up and maintain their youthfulness. But now there appears to be two kinds of blue stragglers. In addition to the vampires, there are also the bad-boys: these blue stragglers steal mass from companion stars by crashing into their neighbors, as if they were in a stellar mosh pit. A team of astronomers used data from the Hubble Space Telescope to study the blue straggler star content in Messier 30, a swarm of several hundred thousand stars located about 28,000 light-years from Earth.

This wide-field image of the sky around the globular cluster Messier 30 was created from photographs forming part of the Digitized Sky Survey 2. Located about 28 000 light-years away from Earth, this cluster -- a swarm of several hundred thousand stars -- is about 90 light-years across. The field of view is approximately 2.9 degrees across. Credit: ESO and Digitized Sky Survey 2 Acknowledgment: Davide De Martin
This wide-field image of the sky around the globular cluster Messier 30 was created from photographs forming part of the Digitized Sky Survey 2. Located about 28 000 light-years away from Earth, this cluster -- a swarm of several hundred thousand stars -- is about 90 light-years across. The field of view is approximately 2.9 degrees across. Credit: ESO and Digitized Sky Survey 2 Acknowledgment: Davide De Martin

Blue stragglers have been known since the early 1950s, but how they formed remains an astrophysical puzzle. Of all the stars in Messier 30, which formed about 13 billion years ago, a small fraction of them appeared to be significantly younger.

“It’s like seeing a few kids in a group photo of residents of a retirement home, and ask, ‘How did they get there?'” said Alison Sills, assistant professor at McMaster University. “In short, we seem to have found that there are two fountains of youth for stars.”

Previously, it was thought that that the less massive star in a binary system acts as a “vampire”, siphoning fresh hydrogen from its more massive companion star that allows the smaller star to heat up, growing bluer and hotter. However, the new study shows that some of the blue stragglers have instead been rejuvenated by a sort of “cosmic facelift”, courtesy of cosmic collisions. These stellar encounters are nearly head-on collisions in which the stars actually merge, mixing their nuclear fuel and re-stoking the fires of nuclear fusion. Merged stars and binary systems would both be about twice the typical mass of individual stars in the cluster.
This illustration demonstrates the two ways that blue stragglers — or "rejuvenated" stars — in globular clusters form. Credit: NASA/ESA
“The observations, which agree with our models, demonstrate that blue stragglers formed by collisions have slightly different properties from those formed by vampirism. This provides a direct demonstration that the two formation scenarios are valid and that they are both operating simultaneously in this cluster,” said Sills, who was part of an international steam that made the findings.

Using data from the now-retired Wide Field Planetary Camera 2 (WFPC2) aboard Hubble, astronomers found that these “straggling” stars are much more concentrated towards the center of the cluster than the average star.

The central regions of high density globular clusters are crowded neighborhoods where interactions between stars are nearly inevitable. Researchers conjecture that one or two billion years ago, Messier 30 underwent a major “core collapse” that started to throw stars towards the centre of the cluster, leading to a rapid increase in the density of stars. This event significantly increased the number of collisions among stars, and favored the formation of one of the families of blue stragglers. On the other hand, the increase of stellar crowding due to the collapse of the core also perturbed the twin systems, encouraging the vampirism phenomenon and thus forming the other family of blue stragglers.

The study will be published in the Dec. 24 issue of Nature.

Sources: ESA Hubble Information, Center, McMaster University University of Wisconsin/Madison

Posted on by Nancy Atkinson

Hubble Finds Smallest Kuiper Belt Object Ever Seen

Artists impression of a small KBO detected by Hubble as it transited a star. Credit: NASA, ESA, and G. Bacon (STScI)

Like finding a needle in a haystack, the Hubble Space Telescope has discovered the smallest object ever seen in visible light in the Kuiper Belt. While Hubble didn’t image this KBO directly, its detection is still quite impressive. The object is only 975 meters (3,200 feet) across and a whopping 6.7 billion kilometers (4.2 billion miles) away. The smallest Kuiper Belt Object (KBO) seen previously in reflected light is roughly 48 km (30 miles) across, or 50 times larger. This provides the first observational evidence for a population of comet-sized bodies in the Kuiper Belt.

The object detected by Hubble is so faint — at 35th magnitude — it is 100 times dimmer than what Hubble can see directly.

So then how did the space telescope uncover such a small body? The telltale signature of the small vagabond was extracted from Hubble’s pointing data, not by direct imaging. When the object passed in front a of star, Hubble’s instruments picked up the occulation.

Hubble has three optical instruments called Fine Guidance Sensors (FGS). The FGSs provide high-precision navigational information to the space observatory’s attitude control systems by looking at select guide stars for pointing. The sensors exploit the wavelike nature of light to make precise measurement of the location of stars.

Illustration of how Hubble found a tiny KBO. Credit: NASA, ESA, and A. Feild (STScI)
Illustration of how Hubble found a tiny KBO. Credit: NASA, ESA, and A. Feild (STScI)

In details of a paper published in the December 17th issue of the journal Nature, Hilke Schlichting of the California Institute of Technology in Pasadena, Calif., and her collaborators determined that the FGS instruments are so good that they can see the effects of a small object passing in front of a star. This would cause a brief occultation and diffraction signature in the FGS data as the light from the background guide star was bent around the intervening foreground KBO.

They selected 4.5 years of FGS observations for analysis. Hubble spent a total of 12,000 hours during this period looking along a strip of sky within 20 degrees of the solar system’s ecliptic plane, where the majority of KBOs should dwell. The team analyzed the FGS observations of 50,000 guide stars in total.

Scouring the huge database, Schlichting and her team found a single 0.3-second-long occultation event. This was only possible because the FGS instruments sample changes in starlight 40 times a second. The duration of the occultation was short largely because of the Earth’s orbital motion around the Sun.

They assumed the KBO was in a circular orbit and inclined 14 degrees to the ecliptic. The KBO’s distance was estimated from the duration of the occultation, and the amount of dimming was used to calculate the size of the object. “I was very thrilled to find this in the data,” says Schlichting.

Hubble observations of nearby stars show that a number of them have Kuiper Belt–like disks of icy debris encircling them. These disks are the remnants of planetary formation. The prediction is that over billions of years the debris should collide, grinding the KBO-type objects down to ever smaller pieces that were not part of the original Kuiper Belt population. The Kuiper Belt is therefore collisionally evolving, meaning that the region’s icy content has been modified over the past 4.5 billion years.

The finding is a powerful illustration of the capability of archived Hubble data to produce important new discoveries. In an effort to uncover additional small KBOs, the team plans to analyze the remaining FGS data for nearly the full duration of Hubble operations since its launch in 1990.

Source: HubbleSite