Photo of the moment
Table of contents
- The tell-tale signs of a galactic merger
- The mouth of the beast: VLT images cometary globule CG4
- ‘Yellowballs’ are part of the development of massive star
- Bubbles from the galactic center: A key to understanding dark matter and our galaxy’s past?
- Ancient skull shows modern humans colonized Eurasia 60-70,000 years ago
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NGC 7714 is a spiral galaxy at 100 million light-years from Earth — a relatively close neighbour in cosmic terms.
The galaxy has witnessed some violent and dramatic events in its recent past. Tell-tale signs of this brutality can be seen in NGC 7714’s strangely shaped arms, and in the smoky golden haze that stretches out from the galactic centre.
So what caused this disfigurement? The culprit is a smaller companion named NGC 7715, which lies just out of the frame of this image — but is visible in the wider-field DSS image. The two galaxies* drifted too close together between 100 and 200 million years ago, and began to drag at and disrupt one another’s structure and shape.
As a result, a ring and two long tails of stars have emerged from NGC 7714, creating a bridge between the two galaxies. This bridge acts as a pipeline, funnelling material from NGC 7715 towards its larger companion and feeding bursts of star formation. Most of the star-forming activity is concentrated at the bright galactic centre, although the whole galaxy is sparking new stars.
Astronomers characterise NGC 7714 as a typical Wolf-Rayet starburst galaxy. This is due to the stars within it; a large number of the new stars are of the Wolf-Rayet type extremely hot and bright stars that begin their lives with dozens of times the mass of the Sun, but lose most of it very quickly via powerful winds.
This Hubble image is a composite of data capturing a broad range of wavelengths, revealing the correlation of the gas clouds and stars in the galaxy. This new picture not only reveals the intricate structure of NGC 7714, but also shows many other objects that are much further away. These background galaxies resemble faint smudges of light, some of them with spiral forms.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
* The interacting pair formed by NGC 7714 and NGC 7715 is named Arp 284.
The object shown in this new picture, CG4, which is also sometimes referred to as God’s Hand, is one of these cometary globules. It is located about 1300 light-years from Earth in the constellation of Puppis (The Poop, or Stern).
The head of CG4, which is the part visible on this image and resembles the head of the gigantic beast, has a diameter of 1.5 light-years. The tail of the globule — which extends downwards and is not visible in the image — is about eight light-years long. By astronomical standards this makes it a comparatively small cloud.
The relatively small size is a general feature of cometary globules. All of the cometary globules found so far are isolated, relatively small clouds of neutral gas and dust within the Milky Way, which are surrounded by hot ionised material.
The head part of CG4 is a thick cloud of gas and dust, which is only visible because it is illuminated by the light from nearby stars. The radiation emitted by these stars is gradually destroying the head of the globule and eroding away the tiny particles that scatter the starlight. However, the dusty cloud of CG4 still contains enough gas to make several Sun-sized stars and indeed, CG4 is actively forming new stars, perhaps triggered as radiation from the stars powering the Gum Nebula reached CG4.
Why CG4 and other cometary globules have their distinct form is still a matter of debate among astronomers and two theories have developed. Cometary globules, and therefore also CG4, could originally have been spherical nebulae, which were disrupted and acquired their new, unusual form because of the effects of a nearby supernova explosion. Other astronomers suggest, that cometary globules are shaped by stellar winds and ionising radiation from hot, massive OB star. These effects could first lead to the bizarrely (but appropriately!) named formations known as elephant trunks and then eventually cometary globules.
To find out more, astronomers need to find out the mass, density, temperature, and velocities of the material in the globules. These can be determined by the measurements of molecular spectral lines which are most easily accessible at millimetre wavelengths — wavelengths at which telescopes like the Atacama Large Millimeter/submillimeter Array (ALMA) operate.
This picture comes from the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.
“Any ideas what these bright yellow fuzzy objects are?” the volunteer wrote on a project message board.
Well, that sparked some discussion among the professional astronomers on the Milky Way Project and eventually led to a study of the compact objects now known as “yellowballs.” A paper just published by The Astrophysical Journal (“The Milky Way Project: What are Yellowballs?”) answers some questions about the 900 yellowballs tagged by citizen scientists.
Charles Kerton, an Iowa State University associate professor of physics and astronomy and a member of the Milky Way Project science team, is first author of the paper. Co-authors are Grace Wolf-Chase of the Adler Planetarium in Chicago and the University of Chicago; Kim Arvidsson, formerly an Iowa State doctoral student and now of Schreiner University in Kerrville, Texas; and Chris Lintott and Robert Simpson of the University of Oxford in the United Kingdom.
“In this paper, through a combination of catalog cross-matching and infrared color analysis, we show that yellowballs are a mix of compact star-forming regions,” the astronomers wrote.
And, they wrote, the project demonstrates “the serendipitous nature of citizen science efforts” because Milky Way Project volunteers “went beyond their assigned tasks and started tagging and discussing” the yellowballs.
The Milky Way Project is part of the Zooniverse, a collection of Internet-based science projects that ask for the public’s help looking through images and other data.
The Milky Way Project asks people to study tens of thousands of Spitzer’s infrared images. People are asked to circle and classify various objects, including bubbles of gas and dust blown by the radiation and charged particles from bright young stars.
To date, citizen scientists have made nearly 1.5 million classifications for the project.
Kerton said all of that classifying is helping astronomers study and map star formation within the galaxy.
But the project took a little detour when citizen scientists noticed yellow objects along the rims of some bubble formations. (It should be noted the yellowballs found in Spitzer’s infrared images aren’t really yellow. When the images are made, various colors are assigned to represent different wavelengths of infrared light. The yellow color on the images highlights where infrared emission from molecules (colored green) and from hot dust (colored red) completely overlap.)
The astronomers began studying those yellowballs by cross-matching them against existing catalogs of space objects. They also studied the luminosity and physical sizes of 138 of the yellowballs.
Kerton said the researchers found most of the yellowballs were located in regions of the galaxy containing dense gas. They also found that yellowball luminosity was consistent with the luminosity expected for a collection of newly formed massive stars.
They’ve concluded there’s an early “yellowball stage” in the formation of stars 10 to 40 times as massive as our sun. The yellowballs are considered very young versions of the bubble formations.
“All massive stars probably go through this yellowball stage,” Kerton said. “The most massive stars go through this stage very early and quickly. Less massive stars go through this stage more slowly.”
The astronomers also wrote that further studies of yellowballs will improve our understanding of how regions of massive star formation grow from early compact stages to more evolved and bubble-like structures.
But those findings aren’t the only highlight of this particular study, Kerton said.
“The fun thing about this study is the involvement of the citizen scientists,” he said. “This is a nice example of people looking at something in the universe and saying, ‘That’s different,’ and then passing it on to professional astronomers.”
Reference: C. R. Kerton, G. Wolf-Chase, K. Arvidsson, C. J. Lintott, R. J. Simpson. THE MILKY WAY PROJECT: WHAT ARE YELLOWBALLS? The Astrophysical Journal, 2015; 799 (2): 153 DOI: 10.1088/0004-637X/799/2/153
Fresh from giving the January 6 Rossi Prize lecture at the Winter American Astronomical Society meeting, three physicists who discovered the Fermi bubbles — Douglas Finkbeiner, Tracy Slatyer and Meng Su — spoke with The Kavli Foundation, revealing that studies of the Fermi bubbles may offer insight into the history of our galaxy. With more study, they could also help in the hunt for dark matter.
“It now seems that, in the past, our black hole was tens of millions of times more active than it is currently,” said Meng Su, a Pappalardo Fellow and an Einstein Fellow at the Massachusetts Institute of Technology and the MIT Kavli Institute for Astrophysics and Space Research. “Before the discovery of Fermi bubbles, people were discussing that possibility, but there was no single piece of evidence showing that our black hole could be that active. The Fermi bubble discovery changed the picture.”
Similar bubbles can be seen in other galaxies, but it’s still impossible to say whether the Fermi bubbles were produced by the same mechanism as the others, Meng continued. That’s because while the Fermi bubbles shine bright in high-energy gamma rays, bubbles in other galaxies are so far away that their gamma rays cannot be seen from Earth. Instead, the distant bubbles are observed in X-rays, radio and microwaves. Future, more precise measurements of the Fermi bubbles in many wavelengths of light may offer insight into how they compare to bubbles in other galaxies, and could help uncover events that took place in our galaxy’s core over the past three to four million years.
But that’s not all. Further study of the Fermi bubbles, which the astrophysicists first discovered when looking for dark matter, may in fact help identify dark matter. That’s because the center of the galaxy, from whence the bubbles originate, is thought to be one of the best places to find evidence of dark matter. Such evidence could be detected as an excess of gamma rays, produced when dark matter particles interact with one another. To find that excess, astrophysicists will need to thoroughly understand the Fermi bubbles. That understanding will allow the researchers to confidently subtract the gamma rays emitted by the Fermi bubbles from the overall gamma-ray signal before looking for an excess of gamma rays coming from dark matter.
In some of the most accepted models of dark matter, “we expect the signals from the galactic center to be significantly brighter than anywhere else in the sky,” said Tracy Slatyer, an assistant professor of physics at the Massachusetts Institute of Technology and an Affiliated Faculty member at the MIT Kavli Institute for Astrophysics and Space Research. “So just giving up on the galactic center is not generally a good option.”
Indeed, Slatyer continued, there are already hints of dark matter appearing in gamma-ray maps of the galactic center — hints that may eventually lead to the discovery of dark matter.
Douglas Finkbeiner, a professor of astronomy and of physics at Harvard University and a member of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, agreed.
“It would be a supreme irony if we found the Fermi bubbles while looking for dark matter and then while studying the Fermi bubbles we discovered dark matter,” he said.
Until now. The discovery in the Manot Cave of Israel’s Western Galilee of an almost complete skull dating back 55,000 years provides direct anatomical evidence that fills the historic time gap of modern human migration into Europe. It is also the first proof that anatomically modern humans existed at the same time as Neanderthals in the same geographical area.
The finding, by Prof. Israel Hershkovitz, the Tassia and Dr. Joseph Meychan Chair for the History and Philosophy of Medicine at the Department of Anatomy and Anthropology at TAU’s Sackler Faculty of Medicine and Head of The Dan David Laboratory for the Search and Study of Modern Humans at the Steinhardt Museum of Natural History and National Research Center, was published in Nature this week.
A new light on our ancestors
“The morphology of the skull indicates that it is that of a modern human of African origin, bearing characteristics of early European Upper Palaeolithic populations. This suggests that the Levantine populations were ancestral to earlier European populations,” said Prof. Hershkovitz. “This study also provides important clues regarding the likely inbreeding between anatomically modern humans and Neanderthals.”
The Manot Cave, where the skull was unearthed, was discovered accidentally in 2008 when a bulldozer struck the cave roof, revealing a time capsule tens of thousands of years old. “This is a goldmine,” said Prof. Hershkovitz. “Most other caves are ‘disturbed caves,’ but this is untouched, frozen in time — truly an amazing find. Among other artefacts found there, the skull, which we dated to 55,000 years ago using uranium thorium methods, was astonishing. It provides insight into the beginnings of the dispersal of modern humans all over the world.”
According to Prof. Hershkovitz, the skull disproves two major narratives: that all modern human populations are linked to migrations out of Africa 100,000 years ago, and that early European Upper Paleolithic populations interbred with local European Neanderthals. Instead the skull indicates that modern humans met and interbred with Neanderthals in Israel, only to later pass on their genes to the rest of the world. Considering Europe was in the last Ice Age period, its harsh climate rendered it generally inhospitable, so humans from the Levant moved first to Asia, and only later (45,000 ago) to Europe.
Sorting out the contradictions
“This was a wonderful scenario, but there was one problem,” said Prof. Hershkovitz. “Geneticists discovered that present-day human populations were linked to a group of African modern humans who started migrating 70,000 years ago. Accordingly, all previous migrations of modern humans out of Africa were presumed to have reached a dead end, contributing nothing to present-day human life. But this was a prediction based on genetic studies only. No fossils to be found anywhere to back it up.”
The first physical evidence that modern man left Africa 70,000 years ago, stopped in Israel, then moved afterward to Europe came in the form of the newly discovered Manot skull. “This skull dates back 55,000 years, a critical time period,” said Prof. Hershkovitz. “If modern humans indeed moved from Africa 70,000 years ago to Israel, this skull means they settled in the Levant for a long period of time, before moving to Europe (45,000 years ago).
“When we analysed the morphology of Manot skull, we made two important discoveries. First, we found African affinities, confirming that the Manot population originated in Africa. Second, we noted many morphological peculiarities akin to early Upper Paleolitic populations in Europe, which suggest ancestral connections to earlier European populations. All of this confirms that people in Manot came from Africa, stayed in Israel for several thousand years, and later, when weather conditions improved, moved to Europe. The Manot people are indeed the ancestors of European populations.”
A further critical finding was the apparent communication and interbreeding between the local Neanderthals and the Manot Homo sapiens in the Levant — not in Europe, as some anthropologists previously hypothesized. “When the Manot people came to Israel, they encountered a flourishing population of Neanderthals, with whom they must have communicated, shared tools and interbred with,” said Prof. Hershkovitz. “According to our analysis of the skull, which bears a complex mix of archaic and modern characteristics, this was probably the only place on earth where Neanderthals and anatomically modern humans lived side by side for a long period of time.”
Reference: Israel Hershkovitz, Ofer Marder, Avner Ayalon, Miryam Bar-Matthews, Gal Yasur, Elisabetta Boaretto, Valentina Caracuta, Bridget Alex, Amos Frumkin, Mae Goder-Goldberger, Philipp Gunz, Ralph L. Holloway, Bruce Latimer, Ron Lavi, Alan Matthews, Viviane Slon, Daniella Bar-Yosef Mayer, Francesco Berna, Guy Bar-Oz, Reuven Yeshurun, Hila May, Mark G. Hans, Gerhard W. Weber, Omry Barzilai.Levantine cranium from Manot Cave (Israel) foreshadows the first European modern humans. Nature, 2015; DOI: 10.1038/nature14134
“Our three-dimensional map is a rare look at the insides of an exploded star,” says Dan Milisavljevic of the Harvard-Smithsonian Center for Astrophysics (CfA). This research is being published in the Jan. 30 issue of the journal Science.
About 340 years ago a massive star exploded in the constellation Cassiopeia. As the star blew itself apart, extremely hot and radioactive matter rapidly streamed outward from the star’s core, mixing and churning outer debris. The complex physics behind these explosions is difficult to model, even with state-of-the-art simulations run on some of the world’s most powerful supercomputers. However, by carefully studying relatively young supernova remnants like Cas A, astronomers can investigate various key processes that drive these titanic stellar explosions.
“We’re sort of like bomb squad investigators. We examine the debris to learn what blew up and how it blew up,” explains Milisavljevic. “Our study represents a major step forward in our understanding of how stars actually explode.”
To make the 3-D map, Milisavljevic and co-author Rob Fesen of Dartmouth College examined Cas A in near-infrared wavelengths of light using the Mayall 4-meter telescope at Kitt Peak National Observatory, southwest of Tucson, AZ. Spectroscopy allowed them to measure expansion velocities of extremely faint material in Cas A’s interior, which provided the crucial third dimension.
They found that the large interior cavities appear to be connected to — and nicely explain — the previously observed large rings of debris that make up the bright and easily seen outer shell of Cas A. The two most well-defined cavities are 3 and 6 light-years in diameter, and the entire arrangement has a Swiss cheese-like structure.
The bubble-like cavities were likely created by plumes of radioactive nickel generated during the stellar explosion. Since this nickel will decay to form iron, Milisavljevic and Fesen predict that Cas A’s interior bubbles should be enriched with as much as a tenth of a solar mass of iron. This enriched interior debris hasn’t been detected in previous observations, however, so next-generation telescopes may be needed to find the “missing” iron and confirm the origin of the bubbles.
Reference: D. Milisavljevic, R. A. Fesen. The bubble-like interior of the core-collapse supernova remnant Cassiopeia A. Science, 2015; 347 (6221): 526 DOI:10.1126/science.1261949
Qijianglong (pronounced “CHI-jyang-lon”) is about 15 metres in length and lived about 160 million years ago in the Late Jurassic. The name means “dragon of Qijiang,” for its discovery near Qijiang City, close to Chongqing. The fossil site was found by construction workers in 2006, and the digging eventually hit a series of large neck vertebrae stretched out in the ground. Incredibly, the head of the dinosaur was still attached. “It is rare to find a head and neck of a long-necked dinosaur together because the head is so small and easily detached after the animal dies,” explains Miyashita.
The new species belongs to a group of dinosaurs called mamenchisaurids, known for their extremely long necks sometimes measuring up to half the length of their bodies. Most sauropods, or long-necked dinosaurs, have necks only about one third the length of their bodies.
Unique among mamenchisaurids, Qijianglong had neck vertebrae that were filled with air, making their necks relatively lightweight despite their enormous size. Interlocking joints between the vertebrae also indicate a surprisingly stiff neck that was much more mobile bending vertically than sideways, similar to a construction crane.
“Qijianglong is a cool animal. If you imagine a big animal that is half-neck, you can see that evolution can do quite extraordinary things.” says Miyashita.
Mamenchisaurids are only found in Asia, but the discovery of Qijianglong reveals that there could be as many differences among mamenchisaurids as there are between long-necked dinosaurs from different continents.
“Qijianglong shows that long-necked dinosaurs diversified in unique ways in Asia during Jurassic times–something very special was going on in that continent,” says Miyashita. “Nowhere else we can find dinosaurs with longer necks than those in China. The new dinosaur tells us that these extreme species thrived in isolation from the rest of the world.”
Miyashita believes that mamenchisaurids evolved into many different forms when other long-necked dinosaurs went extinct in Asia. “It is still a mystery why mamenchisaurids did not migrate to other continents,” he says. It is possible that the dinosaurs were once isolated as a result of a large barrier such as a sea, and lost in competition with invading species when the land connection was restored later.
The Qijianglong skeleton is now housed in a local museum in Qijiang. “China is home to the ancient myths of dragons,” says Miyashita, “I wonder if the ancient Chinese stumbled upon a skeleton of a long-necked dinosaur like Qijianglong and pictured that mythical creature.”
Reference: Lida Xing, Tetsuto Miyashita, Jianping Zhang, Daqing Li, Yong Ye, Toru Sekiya, Fengping Wang, Philip J. Currie. A new sauropod dinosaur from the Late Jurassic of China and the diversity, distribution, and relationships of mamenchisaurids. Journal of Vertebrate Paleontology, 2015; e889701 DOI:10.1080/02724634.2014.889701
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Astronomers have captured a striking view of spiral galaxy NGC 7714. This galaxy has drifted too close to another nearby galaxy and the dramatic interaction…
Like the gaping mouth of a gigantic celestial creature, the cometary globule CG4 glows menacingly in this new image from ESO’s Very Large Telescope. Although…
Citizen scientists wanted to know: What are the yellow objects on these infrared images from the Spitzer Space Telescope? Astronomers now report that the “yellowballs”…
The astrophysicists who discovered two enormous radiation bubbles in the center of our galaxy discuss what they may tell us about the Milky Way and…