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)


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.

Hammer, et al.
Delgado-Serrano et al.

Source: Space Telescope Institute

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

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

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

Incredible New Hubble Image is Full of Stars!

A brand new Hubble image from Wide Field Camera 3 shows the most detailed view of the largest stellar nursery in our local galactic neighborhood. The massive, young stellar grouping, called R136, is only a few million years old and resides in the 30 Doradus Nebula, a turbulent star-birth region in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. There is no known star-forming region in our galaxy as large or as prolific as 30 Doradus. Many of the diamond-like icy blue stars are among the most massive stars known. Several of them are over 100 times more massive than our Sun. In a few million years, this region should provide an incredible show: that’s when these hefty stars are destined to pop off like a string of firecrackers, as supernovas.

The image, taken in ultraviolet, visible, and red light by Hubble’s Wide Field Camera 3, spans about 100 light-years. The nebula is close enough to Earth that Hubble can resolve individual stars, giving astronomers important information about the birth and evolution of stars in the universe. The Hubble observations were taken Oct. 20-27, 2009. The blue color is light from the hottest, most massive stars; the green from the glow of oxygen; and the red from fluorescing hydrogen.

Ground-based version of the Doradus Constellation. Credit: A. Fujii
Ground-based version of the Doradus Constellation. Credit: A. Fujii

The LMC is located 170,000 light-years away and is a member of the Local Group of Galaxies, which also includes the Milky Way.

Click here for larger (and eye-popping!) versions of this image.

You can also “zoom” in and out of this image here on the “Starry Critters” website.
Source: HubbleSite

Hubble Takes a New “Deep Field” Image with Wide Field Camera 3

Hubble’s latest image is another stunner — and just look at all the galaxies! Hubble has produced a new version of the Ultra Deep Field, this time in near-infrared light and taken with the newly installed Wide Field Camera 3. This is the deepest image yet of the Universe in near-infrared, and so the faintest and reddest objects in the image are likely the oldest galaxies ever identified, and they likely formed only 600–900 million years after the Big Bang. This image was taken in the same region as the visible Ultra Deep Field in 2004, but this new deep view at longer wavelengths provides insights into how galaxies grew in their formative years early in the Universe’s history.

“Hubble has now re-visited the Ultra Deep Field which we first studied 5 years ago, taking infrared images which are more sensitive than anything obtained before,” said Dr. Daniel Stark, a postdoctoral researcher from Cambridge University. “We can now look even further back in time, identifying galaxies when the Universe was only 5 percent of its current age – within 1 billion years of the Big Bang.”

A portion of the Hubble Ultra Deep Field showing the location of a potentially very distant galaxy (marked by crosshairs).   Credit: Oxford University
A portion of the Hubble Ultra Deep Field showing the location of a potentially very distant galaxy (marked by crosshairs). Credit: Oxford University

The image was taken during a total of four days in August 2009, with 173,000 seconds of total exposure time. Since infrared light is invisible to the human eye and therefore does not have colors that can be perceived, the image is a “natural” representation that in shorter infrared wavelengths are represented as blue and the longer wavelengths as red. The faintest objects are about one billion times fainter than the dimmest visible objects seen with the naked eye.

Click here for a video zooming into the Ultra Deep Field.

“The expansion of the Universe causes the light from very distant galaxies to appear more red, so having a new camera on Hubble which is very sensitive in the infrared means we can identify galaxies at much greater distances than previously possible,” said Stephen Wilkins, from Oxford University.

Where is the new Ultra Deep Field in the sky?  Credit: HubbleSite
Where is the new Ultra Deep Field in the sky? Credit: HubbleSite

The team that took this image in August of 2009 have made it available for research by astronomers worldwide, and a multitude of astronomers have been furiously searching through the data for the most distant galaxies yet discovered. In just three months, twelve scientific papers on these new data have been submitted.

As well as identifying potentially the most distant objects yet, these new HST observations present an intriguing puzzle. “We know the gas between galaxies in the Universe was ionized (or fried) early in history, but the total light from these new galaxies may not be sufficient to achieve this,” said Andrew Bunker, from the University of Oxford.

Installation of Wide Field Camera 3 by astronauts as part of servicing mission 4. Courtesy of NASA.
Installation of Wide Field Camera 3 by astronauts as part of servicing mission 4. Courtesy of NASA.

“These new observations from HST are likely to be the most sensitive images Hubble will ever take, but the very distant galaxies we have now discovered will be studied in detail by Hubble’s successor, the James Webb Space Telescope, which will be launched in 2014,” said Professor Jim Dunlop at the University of Edinburgh.

1. By R.J. McLure, J.S. Dunlop, M. Cirasuolo, A.M. Koekemoer, E. Sabbi, D.P. Stark, T.A. Targett, R.S. Ellis,

2. By Stephen M. Wilkins, Andrew J. Bunker, Richard S. Ellis, Daniel Stark, Elizabeth R. Stanway, Kuenley Chiu, Silvio Lorenzoni, Matt J. Jarvis

3. By Bunker, Andrew; Wilkins, Stephen; Ellis, Richard; Stark, Daniel; Lorenzoni, Silvio; Chiu, Kuenley; Lacy, Mark; Jarvis, Matt; Hickey, Samantha,

Sources: Oxford University, Space Telescope Center

Pillars of Creation

One of the Hubble Space Telescope's most famous images, the "Pillars of Creation" in the Eagle Nebula. Credit: NASA/ESA

The pillars of creation are a part of the emission nebula, or H II region, M16 (also called the Eagle Nebula).

The iconic Hubble Space Telescope image shown here was taken on April Fool’s Day, 1995, using the WFPC2 camera (you can tell it’s that camera from the W-shaped bite taken out of it). It was snapped as part of a research program by Arizona State University’s Jeff Hester and Paul Scowen, and released to the general public on 2 November (i.e. after the proprietary six-month period was over). Embryonic Stars Emerge from Interstellar “Eggs” – that’s the title of the HubbleSite Press Release; “eggs” is a play on EGGs, Evaporating Gas Globules, “dense, compact pockets of interstellar gas“. Interestingly, the name “pillars of creation” is found only in the image title, and nowhere in the Press Release text!

The pillars of creation – and M16 – are about 7,000 light-years away, and each are several light-years long (of course, there’s no “up” in space, so if you turn the image upside down, you see downward hanging linear features … but ‘stalactites of creation’ just isn’t at all catchy).

This region of M16 has been imaged in the x-ray region of the electromagnetic spectrum, by Chandra, in the infrared by Spitzer, and in infrared hi-def from the ground by the ESO’s VLT ANTU telescope.

Hubble has imaged many similar star-forming regions, complete with their own pillars; for example NGC 602 (in the Small Magellanic Cloud; zooming in on this image is fun – can you spot some of the ‘stalactites of creation’?), NGC 6357 (in our own Milky Way, just a tad further away than M16), and a different pillar (“Stellar Spire”) in the Eagle Nebula. Who knows? Maybe, one day, the Horsehead Nebula may become a pillar of creation too!

Universe Today has many articles on these pillars, Shadows Helped Form the “Pillars of Creation”, The Eagle … Has Arrived, Chandra Gives Another Look at the Pillars of Creation, Spitzer’s Version of the Pillars of Creation, and Eagle Nebula’s Pillars Were Wiped Out Thousands of Years Ago.

The Pillars of Creation also feature in Astronomy Cast episodes Nebulae, Stellar Populations, and Stellar Nurseries.

Countdown to Christmas: Hubble Advent Calendar

This is way cooler than those chocolate filled advent calendars that you can buy at the grocery store (although arguably less yummy): The Big Picture over at The Boston Globe is doing an advent calendar to count down the days until Christmas, only instead of opening a little door to nuggets of chocolate each day, you get huge chunks of Hubble eye candy!

Each day until Christmas you can feast your eyes on a new image from the Hubble Space Telescope like today’s shown above. Hubble has produced enough images over its lifetime to fill a few thousand advent calendars. If you happened to be worried about your waistline this holiday season, forget buying a calorie-bloated advent calendar and head on over to The Big Picture for the next 24 images, which are sure to be stunning.

Little cycling cap tip to The Bad Astronomer

Hubble Sees Dazzling Dust in the Iris Nebula

NGC 7023. Credit: NASA and ESA


Another gorgeous image from Hubble! This close-up of NGC 7023, or the Iris Nebula, shows an area filled with cosmic dust. Illuminated from above by the nearby star HD 200775, the dust resembles pink cotton candy, accentuated with diamond-like stars. The “cotton candy” is actually made up of tiny particles of solid matter, with sizes from ten to a hundred times smaller than those of the dust grains we find on Earth, and the “diamonds” are both background and foreground stars.

The image was taken previous to Hubble’s recent servicing mission, using the Advanced Camera for Surveys. Astronomers also used Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument to try to determine which chemical elements are present in the nebula.

NGC 7023 is a reflection nebula, which means it scatters light from the massive nearby star. Reflection nebulae are different from emission nebulae, which are clouds of gas that are hot enough to emit light themselves. Reflection nebulae tend to appear blue because of the way light scatters, but parts of the Iris Nebula appear unusually red-ish or pink.

See more, including a movie pan of the nebula here.

Eta Carinae- A Naked Eye Enigma

Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI


Eta Carinae is a beast of a star. At more than 100 solar masses and 4 million times the luminosity of our Sun, eta Car balances dangerously on the edge of stellar stability and it’s ultimate fate: complete self-destruction as a supernova. Recently, Hubble Space Telescope observations of the central star in the eta Carinae Nebula have raised an alert on eta Car among the professional community. What they discovered was totally unexpected.

“It used to be, that if you looked at eta Car you saw a nebula and then a faint little core in the middle” said Dr. Kris Davidson, from the University of Minnesota. “Now when you look at it, it’s basically the star with a nebula. The appearance is completely different. The light from the star now accounts for more than half the total output of eta Car. I didn’t expect that to happen until the middle of this century. It’s decades ahead of schedule. We know so little about these very massive objects, that if eta Car becomes a supernova next Thursday we should not be very surprised.”

In 1843, eta Carinae underwent a spectacular eruption, making it the second brightest star in the sky behind Sirius. During this violent episode, eta Car ejected 2 to 3 solar masses of material from the star’s polar regions. This material, traveling at speeds close to 700 km/s, formed two large, bipolar lobes, now known as the Homunculus Nebula. After the great eruption, Eta Car faded, erupted again briefly fifty years later, then settled down, around 8th magnitude. Davidson picks up the story from there.

This light curve depicts the visual apparent brightness of Eta Car from 1822 to date. It contains visual estimates (big circles), photographic (squares), photoelectric (triangles) and CCD (small circles) observations. All of them have been fitted for consistency of the whole data. Red points are recent observations from La Plata (Feinstein 1967; Fernández-Lajús et al., 2009, 2010). Used by permission.
This light curve depicts the visual apparent brightness of Eta Car from 1822 to date. It contains visual estimates (big circles), photographic (squares), photoelectric (triangles) and CCD (small circles) observations. All of them have been fitted for consistency of the whole data. Red points are recent observations from La Plata (Feinstein 1967; Fernández-Lajús et al., 2009, 2010). Used by permission.

“Around 1940, Eta suddenly changed its state. The spectrum changed and the brightness started to increase. Unfortunately, all this happened at a time when almost no one was looking at it. So we don’t know exactly what happened. All we know is that by the 1950’s, the spectrum had high excitation Helium lines in it that it didn’t have before, and the whole object, the star plus the Homunculus, was gradually increasing in brightness. In the past we’ve seen three changes of state. I suspect we are seeing another one happening now.”

During this whole time eta Car has been shedding material via its ferocious stellar winds. This has resulted in an opaque cloud of dust in the immediate vicinity of the star. Normally, this much dust would block our view to the star. So how does Davidson explain this recent, sudden increase in the luminosity of eta Carinae?

“The direct brightening we see is probably the dust being cleared away, but it can’t be merely the expansion of the dust. If it’s clearing away that fast, either something is destroying the dust, or the stellar wind is not producing as much dust as it did before. Personally, I think the stellar wind is decreasing, and the star is returning to the state it was in more than three hundred years ago. In the 1670’s, it was a fourth magnitude, blue, hot star. I think it is returning to that state. Eta Carinae has just taken this long to readjust from its explosion in the 1840’s.”

After 150 years what do we really know about one of the great mysteries of stellar physics? “We don’t understand it, and don’t believe anyone who says they do,” said Davidson.  “The problem is we don’t have a real honest-to-God model, and one of the reasons for that is we don’t have a real honest-to-God explanation of what happened in 1843.”

Can amateur astronomers with modest equipment help untangle the mysteries of eta Carinae? Davidson think so, “The main thing is to make sure everyone in the southern hemisphere knows about it, and anyone with a telescope, CCD or spectrograph should have it pointed at eta Carinae every clear night.”