The curious case of calcium-rich supernovae

NGC 5714
Credit: ESA/Hubble & NASA

This image, captured by the Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope, shows the spiral galaxy NGC 5714, about 130 million light-years away in the constellation of Boötes (the Herdsman). NGC 5714 is classified as a Sc spiral galaxy, but its spiral arms — the dominating feature of spiral galaxies — are almost impossible to see, as NGC 1787 presents itself at an almost perfectly edge-on angle. 

Discovered by William Herschel in 1787, NGC 5714 was host to a fascinating and rare event in 2003. A faint supernova appeared about 8000 light-years below the central bulge of NGC 5714. Supernovae are the huge, violent explosions of dying stars, and the one that exploded in NGC 5714 — not visible in this much later image — was classified as a Type Ib/c supernova and named SN 2003dr. It was particularly interesting because its spectrum showed strong signatures of calcium.

Calcium-rich supernovae are rare and hence of great interest to astronomers. Astronomers still struggle to explain these particular explosions as their existence presents a challenge to both observation and theory. In particular, their appearance outside of galaxies, their lower luminosity compared to other supernovae, and their rapid evolution are still open questions for researchers.

Source: ESA/Hubble/Potw

Dark Matter is a No Show in Ghostly Galaxy

(Left) The ultra-diffuse galaxy is rich with globular clusters, which hold the key to understanding this mysterious object’s origin and mass. (Right) A closer look at one of the globular clusters within the galaxy, which are all much brighter than typically seen, with the brightest emitting almost as much light as the brightest globular cluster within the Milky Way. The spectrum, obtained by Keck Observatory, shows the calcium absorption lines used to determine the velocity of this object. 10 clusters were observed, providing the information needed to determine the mass of the galaxy, revealing its lack of dark matter. Credit:  W.M. Keck Observatory/Gemini Observatory/NSF/AURA/J.Miller/J.Pollard

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Maunakea, Hawaii – Galaxies and dark matter go hand in hand; you typically don’t find one without the other. So when researchers uncovered a galaxy, known as NGC1052-DF2, that is almost completely devoid of the stuff, they were shocked.

“Finding a galaxy without dark matter is unexpected because this invisible, mysterious substance is the most dominant aspect of any galaxy,” said lead author Pieter van Dokkum of Yale University. “For decades, we thought that galaxies start their lives as blobs of dark matter. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. NGC1052-DF2 challenges the standard ideas of how we think galaxies form.”

The research, published in the March 29th issue of the journal Nature, amassed data from Gemini North and W. M. Keck Observatory, both on Maunakea, Hawaii, the Hubble Space Telescope, and other telescopes around the world.

Given its large size and faint appearance, astronomers classify NGC1052-DF2 as an ultra-diffuse galaxy, a relatively new type of galaxy that was first discovered in 2015. These barely visible galaxies are surprisingly common. However, no other galaxy of this type yet-discovered is so lacking in dark matter.

“NGC 1052-DF2 is an oddity, even among this unusual class of galaxy,” said Shany Danieli, a Yale University graduate student on the team.

Van Dokkum and his team first spotted NGC1052-DF2 with the Dragonfly Telephoto Array, a custom-built telescope in New Mexico that they designed to find these ghostly galaxies. NGC1052-DF2 stood out in stark contrast when comparisons were made between images from the Dragonfly Telephoto Array and the Sloan Digital Sky Survey (SDSS). The Dragonfly images show a faint “blob-like” object, while SDSS data reveal a collection of relatively bright point-like sources.

To get a closer look at this inconsistency, the team dissected the light from several of the bright sources within NGC1052-DF2 using Keck Observatory’s Deep Imaging Multi-Object Spectrograph (DEIMOS) and Low-Resolution Imaging Spectrometer (LRIS), identifying 10 globular clusters. These clusters are large compact groups of stars that orbit the galactic core.

The spectral data obtained on the Keck telescopes revealed that the globular clusters were moving much slower than expected. The slower the objects in a system move, the less mass there is in that system. The team’s calculations show that all of the mass in the galaxy could be attributed to the mass of the stars, which means there is almost no dark matter in NGC1052-DF2.

“If there is any dark matter at all, it’s very little,” van Dokkum explained. “The stars in the galaxy can account for all of the mass, and there doesn’t seem to be any room for dark matter.”

“Keck is in a very small group of telescopes that could even attempt these observations, because you need a large telescope to measure these accurate velocities,” van Dokkum added. “Keck also has some of the best spectrographs in the world for measuring the velocities of faint objects. We had the opportunity to check and make sure we got the same result within the uncertainties, and that gave us confidence that we were doing things right.”

To peer even deeper into this unique galaxy, the team used the Gemini-North Multi Object Spectrograph (GMOS) to capture detailed images of NGC1052-DF2, assess its structure, and confirm that the galaxy had no signs of interactions with other galaxies.

“Without the Gemini images dissecting the galaxy’s morphology we would have lacked context for the rest of the data,” said Danieli. “Also, Gemini’s confirmation that NGC1052-DF2 is not currently interacting with another galaxy will help us answer questions about the conditions surrounding its birth.”

The team’s results demonstrate that dark matter is separable from galaxies.

“This discovery shows that dark matter is real – it has its own separate existence apart from other components of galaxies,” said van Dokkum.

NGC1052-DF2’s globular clusters and atypical structure has perplexed astronomers aiming to determine the conditions this galaxy formed under.

“It’s like you take a galaxy and you only have the stellar halo and globular clusters, and it somehow forgot to make everything else,” van Dokkum said. “There is no theory that predicted these types of galaxies. The galaxy is a complete mystery, as everything about it is strange. How you actually go about forming one of these things is completely unknown.”

However, researchers do have some ideas. NGC1052-DF2 resides about 65 million light years away in a collection of galaxies that is dominated by the giant elliptical galaxy NGC 1052. Galaxy formation is turbulent and violent, and van Dokkum suggests that the growth of the fledgling massive galaxy billions of years ago perhaps played a role in NGC1052-DF2’s dark-matter deficiency.

Another idea is that a cataclysmic event within the oddball galaxy, such as the birth of myriad massive stars, swept out all the gas and dark matter, halting star formation.

These possibilities are speculative, however, and don’t explain all of the characteristics of the observed galaxy, the researchers said.

The team continues the hunt for more dark-matter-deficient galaxies. They are analyzing Hubble images of 23 other diffuse galaxies. Three of them appear to share similarities with NGC1052-DF2, which van Dokkum plans to follow up on in the coming months at Keck Observatory.

“Every galaxy we knew about before has dark matter and they all fall in familiar categories like spiral or elliptical galaxies,” van Dokkum said. “But what would you get if there were no dark matter at all? Maybe this is what you would get.”

Source: W.M. Keck Observatory

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Science Contacts

Pieter van Dokkum
Astronomy Department
Yale University
Email: pieter.vandokkum@yale.edu
Phone: (203) 432-5048

Shany Danieli
Astronomy Department
Yale University
Phone: (857) 919-3674
Email: shany.danieli@yale.edu

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Media Contacts

Mari-Ela Chock
W. M. Keck Observatory
Email: mchock@keck.hawaii.edu
Phone: (808) 554-0567

Jasmin Silva
Gemini Observatory
Email: jsilva@gemini.edu
Desk: (808) 974-2575
Cell: (808) 989-7418

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About Deimos

The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity. Support for DEIMOS was generously provided by the National Science Foundation.

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About W.M.Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. 

The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Article Summary

Astronomers using W. M. Keck Observatory and Gemini data in Hawai‘i have encountered a galaxy that appears to have almost no dark matter. Since the Universe is dominated by dark matter, and it is the foundation upon which galaxies are built, “...this is a game changer,” according to Principal Investigator Pieter van Dokkum of Yale University. 

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Chaotic web of filaments in a Milky Way stellar nursery

Chaotic web of filaments in a Milky Way stellar nursery

Copyright ESA/Herschel/PACS, SPIRE/Hi-GAL Project. Acknowledgement: UNIMAP / L. Piazzo, La Sapienza - Università di Roma; E. Schisano / G. Li Causi, IAPS/INAF, Italy. Hi-res image

The plane of the Milky Way is rich in star-forming regions, such as the one pictured in this stunning scene by ESA’s Herschel space observatory. To the far-infrared eye of Herschel, this region reveals an intricate network of gas filaments and dark bubbles interspersed by bright hotspots where new stars come to life. 

The cooler regions, which emit light at longer wavelengths, are displayed in a red-brownish colour. Hotter areas, where star formation is more intense, shine in blue and white tones. Some areas are particularly bright, suggesting a number of luminous, massive stars are forming there.

Particularly striking is the chaotic web of gas filaments we see in this scene. Astronomers think there is a link between star formation and the filamentary structures in the interstellar medium. In the densest strands, the gas that makes up the filaments becomes unstable and forms clumps of material bound together by gravity. If dense enough, these collapsed blobs of gas eventually go on to become newborn stars.

Observations by Herschel showed the filamentary complexity to be ubiquitous in the plane of our Galaxy, from a few to hundreds of light-years. In nearby star-forming clouds, within 1500 light-years of the Sun, these filaments seem to be roughly all the same width – about a third of a light-year. This suggests a common physical mechanism in their origin, possibly linked to the turbulent nature of interstellar gas clouds.

The star-formation region in this image, centred around –70º longitude in galactic coordinates, is located in the Carina neighbourhood, home to the glorious Carina Nebula. Located some 7500 light-years away, Carina is one of the largest clouds of gas and dust in the plane of the Milky Way. It hosts the famous Eta Carinae, one of the most luminous and massive stellar systems in our galaxy. 

Herschel, which operated from 2009 until 2013, was a large space telescope observing in the far-infrared and submillimetre parts of the spectrum. This spectral range is ideal to observe the glow from cool dust in the regions where stars form. As part of Hi-GAL, the Herschel infrared Galactic Plane Survey, the observatory surveyed the plane of our Galaxy, exploring the Milky Way’s star-formation regions in unprecedented detail. This image, a product of Hi-GAL, combines observations at three different wavelengths: 70 microns (blue), 160 microns (green) and 250 microns (red).

Source: ESA/Space in Images

Kepler Solves Mystery of Fast and Furious Explosions

Model for the Creation of a Fast-Evolving Luminous Transient

This illustration shows a proposed model for a mysterious astronomical event called a Fast-Evolving Luminous Transient (FELT). In the left panel, an aging red giant star loses mass via a stellar wind. This balloons into a huge gaseous shell around the star. In the center panel, the massive star’s core implodes to trigger a supernova explosion. In the right panel, the supernova shockwave plows into the outer shell, converting the kinetic energy from the explosion into a brilliant burst of light. The flash of radiation lasts for only a few days — one-tenth the duration of a typical supernova explosion.  Credit:  Illustration: NASA, ESA, and A. Feild (STScI) - Science: NASA, ESA, and A. Rest (STScI).  Release images

The universe is full of mysterious exploding phenomena that go boom in the dark. One particular type of ephemeral event, called a Fast-Evolving Luminous Transient (FELT), has bewildered astronomers for a decade because of its very brief duration.

Now, NASA’s Kepler Space Telescope — designed to go hunting for planets across our galaxy — has also been used to catch FELTs in the act and determine their nature. They appear to be a new kind of supernova that gets a brief turbo boost in brightness from its surroundings.

Kepler's ability to precisely sample sudden changes in starlight has allowed astronomers to quickly arrive at this model for explaining FELTs, and rule out alternative explanations.

Researchers conclude that the source of the flash is from a star after it collapses to explode as a supernova. The big difference is that the star is cocooned inside one or more shells of gas and dust. When the tsunami of explosive energy from the blast slams into the shell, most of the kinetic energy is immediately converted to light. The burst of radiation lasts for only a few days — one-tenth the duration of a typical supernova explosion.

Over the past decade several FELTs have been discovered with timescales and luminosities not easily explained by traditional supernova models. And, only a few FELTs have been seen in sky surveys because they are so brief. Unlike Kepler, which collects data on a patch of sky every 30 minutes, most other telescopes look every few days. Therefore they often slip through undetected or with only one or two measurements, making understanding the physics of these explosions tricky.

In the absence of more data, there have been a variety of theories to explain FELTs: the afterglow of a gamma-ray burst, a supernova boosted by a magnetar (neutron star with a powerful magnetic field), or a failed Type Ia supernova.

Then along came Kepler with its precise, continuous measurements that allowed astronomers to record more details of the FELT event. "We collected an awesome light curve," said Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland. "We were able to constrain the mechanism and the properties of the blast. We could exclude alternate theories and arrive at the dense-shell model explanation. This is a new way for massive stars to die and distribute material back into space.

"With Kepler, we are now really able to connect the models with the data," he continued. "Kepler just makes all the difference here. When I first saw the Kepler data, and realized how short this transient is, my jaw dropped. I said, 'Oh wow!'"

"The fact that Kepler completely captured the rapid evolution really constrains the exotic ways in which stars die. The wealth of data allowed us to disentangle the physical properties of the phantom blast, such as how much material the star expelled at the end of its life and the hypersonic speed of the explosion. This is the first time that we can test FELT models to a high degree of accuracy and really connect theory to observations," said David Khatami of the University of California at Berkeley and Lawrence Berkeley National Laboratory.

This discovery is an unexpected spinoff of Kepler’s unique capability to sample changes in starlight continuously for several months. This capability is needed for Kepler to discover extrasolar planets that briefly pass in front of their host stars, temporarily dimming starlight by a small percent.

The Kepler observations indicate that the star ejected the shell less than a year before it went supernova. This gives insight into the poorly understood death throes of stars — the FELTs apparently come from stars that undergo "near-death experiences" just before dying, belching out shells of matter in mini-eruptions before exploding entirely.

The science team's study appears in the March 26, 2018 online issue of Nature Astronomy.

Rest says the next steps will be to find more of these objects in the ongoing K2 mission, or in the next mission of that kind, TESS. This will allow astronomers to start a follow-up campaign spanning different wavelength regimes, which constrains the nature and physics of this new kind of explosion.

NASA's Ames Research Center at Moffett Field, California, manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace and Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder, Colorado. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, archives, hosts, and distributes Kepler science data. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.


Related Links

This site is not responsible for content found on external links

• The science paper by A. Rest et al.
• NASA's Kepler Feature Story
• NASA's Kepler Portal

Contacts

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu

Armin Rest
Space Telescope Science Institute, Baltimore, Maryland
410-338-4358
arest@stsci.edu

Source: HubbleSite/News

A red, metal-rich relic

 NGC 1277

Credit: NASA, ESA, and M. Beasley (Instituto de Astrofísica de Canarias)

This idyllic scene, packed with glowing galaxies, has something truly remarkable at its core: an untouched relic of the ancient Universe. This relic can be seen in the large galaxy at the centre of the frame, a lenticular galaxy named NGC 1277. This galaxy is a member of the famous Perseus Cluster — one of the most massive objects in the known Universe, located some 220 million light-years from Earth.

NGC 1277 has been dubbed a “relic of the early Universe” because all of its stars appear to have formed about 12 billion years ago. To put this in perspective, the Big Bang is thought to have happened 13.8 billion years ago. Teeming with billions of old, metal-rich stars, this galaxy is also home to many ancient globular clusters: spherical bundles of stars that orbit a galaxy like satellites.

Uniquely, the globuar clusters of NGC 1277 are mostly red and metal-rich — very different to the blue, metal-poor clusters usually seen around similarly-sized galaxies. In astronomy, a metal is any element heavier than hydrogen and helium; these heavier elements are fused together in the hot cores of massive stars and scattered throughout the Universe when these stars explode as they die. In this way, a star’s metal content is related to its age: stars that form later contain greater amounts of metal-rich material, since previous generations of stars have enriched the cosmos from which they are born.

Massive galaxies — and their globular clusters — are thought to form in two phases: first comes an early collapse accompanied by a giant burst of star formation, which forms red, metal-rich clusters, followed by a later accumulation of material, which brings in bluer, metal-poor material. The discovery of NGC 1277’s red clusters confirms that the galaxy is a genuine antique that bypassed this second phase, raising important questions for scientists on how galaxies form and evolve: a hotly debated topic in modern astronomy.

Link

• NASA/STScI release

Source: ESA/Hubble/Potw

Hubble Solves Cosmic 'Whodunit' with Interstellar Forensics

Hubble Measures Content of the Leading Arm of the Magellanic Stream

Credits:Illustration: D. Nidever et al., NRAO/AUI/NSF and A. Mellinger, Leiden-Argentine-Bonn (LAB) Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory, and A. Feild (STScI). Science: NASA, ESA, and A. Fox (STScI).  Release Image

On the outskirts of our galaxy, a cosmic tug-of-war is unfolding—and only NASA’s Hubble Space Telescope can see who’s winning.

The players are two dwarf galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, both of which orbit our own Milky Way Galaxy. But as they go around the Milky Way, they are also orbiting each other. Each one tugs at the other, and one of them has pulled out a huge cloud of gas from its companion.

Called the Leading Arm, this arching collection of gas connects the Magellanic Clouds to the Milky Way. Roughly half the size of our galaxy, this structure is thought to be about 1 or 2 billion years old. Its name comes from the fact that it’s leading the motion of the Magellanic Clouds.

The enormous concentration of gas is being devoured by the Milky Way and feeding new star birth in our galaxy. But which dwarf galaxy is doing the pulling, and whose gas is now being feasted upon? After years of debate, scientists now have the answer to this “whodunit” mystery.

“There’s been a question: Did the gas come from the Large Magellanic Cloud or the Small Magellanic Cloud? At first glance, it looks like it tracks back to the Large Magellanic Cloud,” explained lead researcher Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. “But we’ve approached that question differently, by asking: What is the Leading Arm made of? Does it have the composition of the Large Magellanic Cloud or the composition of the Small Magellanic Cloud?”

Fox’s research is a follow-up to his 2013 work, which focused on a trailing feature behind the Large and Small Magellanic Clouds. This gas in this ribbon-like structure, called the Magellanic Stream, was found to come from both dwarf galaxies. Now Fox wondered about its counterpart, the Leading Arm. Unlike the trailing Magellanic Stream, this tattered and shredded “arm” has already reached the Milky Way and survived its journey to the galactic disk.

The Leading Arm is a real-time example of gas accretion, the process of gas falling onto galaxies. This is very difficult to see in galaxies outside the Milky Way, because they are too far away and too faint. “As these two galaxies are in our backyard, we essentially have a front-row seat to view the action,” said collaborator Kat Barger at Texas Christian University.

In a new kind of forensics, Fox and his team used Hubble’s ultraviolet vision to chemically analyze the gas in the Leading Arm. They observed the light from seven quasars, the bright cores of active galaxies that reside billions of light-years beyond this gas cloud. Using Hubble’s Cosmic Origins Spectrograph, the scientists measured how this light filters through the cloud.

In particular, they looked for the absorption of ultraviolet light by oxygen and sulfur in the cloud. These are good gauges of how many heavier elements reside in the gas. The team then compared Hubble’s measurements to hydrogen measurements made by the National Science Foundation’s Robert C. Byrd Green Bank Telescope at the Green Bank Observatory in West Virginia, as well as several other radio telescopes.

“With the combination of Hubble and Green Bank Telescope observations, we can measure the composition and velocity of the gas to determine which dwarf galaxy is the culprit,” explained Barger.

After much analysis, the team finally had conclusive chemical “fingerprints” to match the origin of the Leading Arm’s gas. “We’ve found that the gas matches the Small Magellanic Cloud,” said Fox. “That indicates the Large Magellanic Cloud is winning the tug-of-war, because it has pulled so much gas out of its smaller neighbor.”

This answer was possible only because of Hubble’s unique ultraviolet capability. Because of the filtering effects of Earth’s atmosphere, ultraviolet light cannot be studied from the ground. “Hubble is the only game in town,” explained Fox. “All the lines of interest, including oxygen and sulfur, are in the ultraviolet. So if you work in the optical and infrared, you can’t see them.”

Gas from the Leading Arm is now crossing the disk of our galaxy. As it crosses, it interacts with the Milky Way’s own gas, becoming shredded and fragmented.

This is an important case study of how gas gets into galaxies and fuels star birth. Astronomers use simulations and try to understand the inflow of gas in other galaxies. But here, the gas is being caught red-handed as it moves across the Milky Way’s disk. Sometime in the future, planets and solar systems in our galaxy may be born out of material that used to be part of the Small Magellanic Cloud.

The team’s study appears in the Feb. 20 issue of The Astrophysical Journal.

As Fox and his team look ahead, they hope to map out the full size of the Leading Arm—something that is still unknown.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

Related Links

This site is not responsible for content found on external links

• The science paper by A. Fox et al.
• NASA's Hubble Portal

Contact

Ann Jenkins / Ray Villard 
Space Telescope Science Institute, Baltimore, Maryland 
410-338-4488 / 410-338-4514 
jenkins@stsci.edu / villard@stsci.edu

Andrew Fox
Space Telescope Science Institute, Baltimore, Maryland 
410-338-5083
afox@stsci.edu

Source: HubbleSite/News 

Double or Nothing: Astronomers Rethink Quasar Environment

Figure 1: Galaxy distribution and close-ups of some protoclusters revealed by HSC. Higher- and lower-density regions are represented by redder and bluer colors, respectively. In the close-ups, white circles indicate the positions of distant galaxies. The red regions are expected to evolve into galaxy clusters. From the close-ups, we can see various morphologies of the overdense regions: some have another neighboring overdense region, or are elongated like a filament, while there are also isolated overdense regions. (Credit: NAOJ)

Figure 2: The two quasar pairs and surrounding galaxies. Stars indicate quasars and bright (faint) galaxies at the same epoch are shown as circles (dots). The galaxy overdensity with respect to the average density is shown by the contour. The pair members are associated with high density regions of galaxies. (Credit: NAOJ)

Using Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope, astronomers have identified nearly 200 "protoclusters," the progenitors of galaxy clusters, in the early Universe, about 12 billion years ago, about ten times more than previously known. They also found that quasars don't tend to reside in protoclusters; but if there is one quasar in a protocluster, there is likely a second nearby. This result raises doubts about the relation between protoclusters and quasars.

In the Universe, galaxies are not distributed uniformly. There are some places, known as clusters, where dozens or hundreds of galaxies are found close together. Other galaxies are isolated. To determine how and why clusters formed, it is critical to investigate not only mature galaxy clusters as seen in the present Universe but also observe protoclusters, galaxy clusters in the process of forming.

Because the speed of light is finite, observing distant objects allows us to look back in time. For example, the light from an object 1 billion light-years away was actually emitted 1 billion years ago and has spent the time since then traveling through space to reach us. By observing this light, astronomers can see an image of how the Universe looked when that light was emitted.

Even when observing the distant (early) Universe, protoclusters are rare and difficult to discover. Only about 20 were previously known. Because distant protoclusters are difficult to observe directly, quasars are sometimes used as a proxy. When a large volume of gas falls towards the super massive black hole in the center of a galaxy, it collides with other gas and is heated to extreme temperatures. This hot gas shines brightly and is known as a quasar. The thought was that when many galaxies are close together, a merger, two galaxies colliding and melding together, would create instabilities and cause gas to fall into the super massive black hole in one of the galaxies, creating a quasar. However, this relationship was not confirmed observationally due to the rarity of both quasars and protoclusters.

In order to understand protoclusters in the distant Universe a larger observational sample was needed. A team including astronomers from the National Astronomical Observatory of Japan, the University of Tokyo, the Graduate University for Advanced Studies, and other institutes is now conducting an unprecedented wide-field systematic survey of protoclusters using the Subaru Telescope's very wide-field camera, Hyper Suprime-Cam (HSC). By analyzing the data from this survey, the team has already identified nearly 200 regions where galaxies are gathering together to form protoclusters in the early Universe 12 billion years ago.

The team also addressed the relationship between protoclusters and quasars. The team sampled 151 luminous quasars at the same epoch as the HSC protoclusters and to their surprise found that most of those quasars are not close to the overdense regions of galaxies. In fact, their most luminous quasars even avoid the densest regions of galaxies. These results suggest that quasars are not a good proxy for protoclusters and more importantly, mechanisms other than galactic mergers may be needed to explain quasar activity. Furthermore, since they did not find many galaxies near the brightest quasars, that could mean that hard radiation from a quasar suppresses galaxy formation in its vicinity.

On the other hand, the team found two "pairs" of quasars residing in protoclusters. Quasars are rare and pairs of them are even rarer. The fact that both pairs were associated with protoclusters suggests that quasar activity is perhaps synchronous in protocluster environments. "We have succeeded in discovering a number of protoclusters in the distant Universe for the first time and have witnessed the diversity of the quasar environments thanks to our wide-and-deep observations with HSC," says the team's leader Nobunari Kashikawa (NAOJ).

"HSC observations have enabled us to systematically study protoclusters for the first time." says Jun Toshikawa, lead author of the a paper reporting the discovery of the HSC protoclusters, "The HSC protoclusters will steadily increase as the survey proceeds. Thousands of protoclusters located 12 billion light-years away will be found by the time the observations finish. With those new observations we will clarify the growth history of protoclusters."

These results were published on January 1, 2018 in the HSC special issue of the Publications of the Astronomical Society of Japan (Toshikawa et al. 2018, "GOLDRUSH. III. A Systematic Search of Protoclusters at z~4 Based on the >100 deg2 Area", PASJ, 70, S12; Uchiyama et al. 2018, "Luminous Quasars Do Not Live in the Most Overdense Regions of Galaxies at z~4", PASJ, 70, S32; Onoue et al. 2018, "Enhancement of Galaxy Overdensity around Quasar Pairs at z less than 3.6 based on the Hyper Suprime-Cam Subaru Strategic Program Survey", PASJ, 70, S31). These projects are supported by Grants-In-Aid JP15H03645, JP15K17617, and JP15J02115.

 Source: Subaru Telescope

News Center Beyond the WIMP: Unique Crystals Could Expand the Search for Dark Matter

A computerized simulation of the large-scale distribution of dark matter in the universe. An overlay graph (in white) shows how a crystal sample intensely scintillates, or glows, when exposed to X-rays during a lab test. This and other properties could make it a good material for a dark matter detector. Credit: Millennium Simulation, Berkeley Lab.   Hi-res image

A new particle detector design proposed at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) could greatly broaden the search for dark matter – which makes up 85 percent of the total mass of the universe yet we don’t know what it’s made of – into an unexplored realm.

While several large physics experiments have been targeting theorized dark matter particles called WIMPs, or weakly interacting massive particles, the new detector design could scan for dark matter signals at energies thousands of times lower than those measurable by more conventional WIMP detectors.

The ultrasensitive detector technology incorporates crystals of gallium arsenide that also include the elements silicon and boron. This combination of elements causes the crystals to scintillate, or light up, in particle interactions that knock away electrons.

This scintillation property of gallium arsenide has been largely unexplored, said Stephen Derenzo, a senior physicist in the Molecular Biophysics and Integrated Bioimaging Division at Berkeley Lab and lead author of a study published March 20 in the Journal of Applied Physics that details the material’s properties.

“It’s hard to imagine a better material for searching in this particular mass range,” Derenzo said, which is measured in MeV, or millions of electron volts. “It ticks all of the boxes. We are always worried about a ‘Gotcha!’ or showstopper. But I have tried to think of some way this detector material can fail and I can’t.”

The breakthrough came from Edith Bourret, a senior staff scientist in Berkeley Lab’s Materials Sciences Division who decades earlier had researched gallium arsenide’s potential use in circuitry. She gave him a sample of gallium arsenide from this previous work that featured added concentrations, or “dopants,” of silicon and boron.

Derenzo had previously measured some lackluster performance in a sample of commercial-grade gallium arsenide. But the sample that Bourret handed him exhibited a scintillation luminosity that was five times brighter than in the commercial material, owing to the silicon and boron that imbued the material with new and enhanced properties. This enhanced scintillation meant it was far more sensitive to electronic excitations.

“If she hadn’t handed me this sample from more than 20 years ago, I don’t think I would have pursued it,” Derenzo said. “When this material is doped with silicon and boron, this turns out to be very important and, accidentally, a very good choice of dopants.”

Derenzo noted that he has had a longstanding interest in scintillators that are also semiconductors, as this class of materials can produce ultrafast scintillation useful for medical imaging applications such as PET (positron emission tomography) and CT (computed tomography) scans, for example, as well as for high-energy physics experiments and radiation detection.

The doped gallium arsenide crystals he studied appear well-suited for high-sensitivity particle detectors because extremely pure crystals can be grown commercially in large sizes, the crystals exhibit a high luminosity in response to electrons booted away from atoms in the crystals’ atomic structure, and they don’t appear to be hindered by typical unwanted effects such as signal afterglow and dark current signals.

Some of the larger WIMP-hunting detectors – such as that of the Berkeley Lab-led LUX-ZEPLIN project now under construction in South Dakota, and its predecessor, the LUX experiment – incorporate a liquid scintillation detector. A large tank of liquid xenon is surrounded by sensors to measure any light and electrical signals expected from a dark matter particle’s interaction with the nucleus of a xenon atom. That type of interaction is known as a nuclear recoil.

A crystal of gallium arsenide

Credit: Wikimedia Commons

In contrast, the crystal-based gallium arsenide detector is designed to be sensitive to the slighter energies associated with electron recoils – electrons ejected from atoms by their interaction with dark matter particles. As with LUX and LUX-ZEPLIN, the gallium arsenide detector would need to be placed deep underground to shield it from the typical bath of particles raining down on Earth.

It would also need to be coupled to light sensors that could detect the very few infrared photons (particles of light) expected from a low-mass dark matter particle interaction, and the detector would need to be chilled to cryogenic temperatures. The silicon and boron dopants could also possibly be optimized to improve the overall sensitivity and performance of the detectors.

Because dark matter’s makeup is still a mystery – it could be composed of one or many particles of different masses, for example, or may not be composed of particles at all – Derenzo noted that gallium arsenide detectors provide just one window into dark matter particles’ possible hiding places.

While WIMPs were originally thought to inhabit a mass range measured in billions of electron volts, or GeV, the gallium arsenide detector technology is well-suited to detecting particles in the mass range measured in millions of electron volts, or MeV.

Berkeley Lab physicists are also proposing other types of detectors to expand the dark matter search, including a setup that uses an exotic state of chilled helium known as superfluid helium to directly detect low-mass dark matter particles.

“Superfluid helium is scientifically complementary to gallium arsenide since helium is more sensitive to dark matter interactions with atomic nuclei, while gallium arsenide is sensitive to dark matter interacting with electrons,” said Dan McKinsey, a faculty senior scientist at Berkeley Lab and physics professor at UC Berkeley who is a part of the LZ Collaboration and is conducting R&D on dark matter detection using superfluid helium.

“We don’t know whether dark matter interacts more strongly with nuclei or electrons – this depends on the specific nature of the dark matter, which is so far unknown,” he said.

Another effort would employ gallium arsenide crystals in a different approach to the light dark matter search based on vibrations in the atomic structure of the crystals, known as optical phonons. This setup could target “light dark photons,” which are theorized low-mass particles that would serve as the carrier of a force between dark matter particles – analogous to the conventional photon that carries the electromagnetic force.

Still another next-gen experiment, known as the Super Cryogenic Dark Matter Search experiment, or SuperCDMS SNOLAB, will use silicon and germanium crystals to hunt for low-mass WIMPs.

“These would be complementary experiments,” Derenzo said of the many approaches. “We need to look at all of the possible mass ranges. You don’t want to be fooled. You can’t exclude a mass range if you don’t look there.”

Stephen Hanrahan, a staff scientist in Berkeley Lab’s Molecular Biophysics and Integrated Bioimaging Division; and Gregory Bizarri, a senior lecturer in manufacturing at Cranfield University in the U.K., also participated in this study. The work was supported by Advanced Crystal Technologies Inc.

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Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Source: Berkeley Lab/News Center

‘Oumuamua likely came from a binary star system

Artist’s impression of ‘Oumuamua 

Credit: ESO / M. Kornmesser

New research finds that 'Oumuamua, the rocky object identified as the first confirmed interstellar asteroid, very likely came from a binary star system.

A binary star system, unlike our Sun, is one with two stars orbiting a common centre.

For the new study, published in the journal Monthly Notices of the Royal Astronomical Society, Jackson and his co-authors set about testing how efficient binary star systems are at ejecting objects. They also looked at how common these star systems are in the Galaxy.

They found that rocky objects like 'Oumuamua are far more likely to come from binary than single star systems. They were also able to determine that rocky objects are ejected from binary systems in comparable numbers to icy objects.

"It's really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids," says Jackson, who specializes in planet and solar system formation.

Once they determined that binary systems are very efficient at ejecting rocky objects, and that a sufficient number of them exist, they were satisfied that 'Oumuamua very likely came from a binary system. They also concluded that it probably came from a system with a relatively hot, high mass star since such a system would have a greater number of rocky objects closer in.

The team suggest that the asteroid was very likely to have been ejected from its binary system sometime during the formation of planets.

'Oumuamua, which is Hawaiian for 'scout', was first spotted by the Haleakala Observatory in Hawaii on 19 October 2017. With a radius of 200 metres and travelling at a blistering speed of 30 kilometres per second, at its closest it was about 33,000,000 km from Earth.

When it was first discovered researchers initially assumed the object was a comet, one of countless icy objects that release gas when they warm up on approaching the Sun. But it didn't show any comet-like activity as it neared the Sun, and was quickly reclassified as an asteroid, meaning it was rocky.

Researchers were also fairly sure it was from outside our Solar System, based on its trajectory and speed. An eccentricity of 1.2 – which classifies its path as an open-ended hyperbolic orbit – and such a high speed meant it was not bound by the gravity of the Sun.

In fact, as Jackson points out, 'Oumuamua's orbit has the highest eccentricity ever observed in an object passing through our Solar System.

Major questions about ‘Oumuamua remain. For planetary scientists like Jackson, being able to observe objects like these may yield important clues about how planet formation works in other star systems.

“The same way we use comets to better understand planet formation in our own Solar System, maybe this curious object can tell us more about how planets form in other systems.”

Source:  Royal Astronomical Society (RAS)/News and Press

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Media Contact

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7292 3979
Mob: +44 (0)7802 877 699
press@ras.ac.uk

Dr Morgan Hollis
Royal Astronomical Society
Tel: +44 (0)20 7292 3977
Mob: +44 (0)7802 877 700
press@ras.ac.uk

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Science Contact

Dr Alan Jackson
CPS Postdoctoral Fellow
Centre for Planetary Sciences
University of Toronto
Tel: +1 416 208 5099 (4 hours behind GMT)
ajackson@cita.utoronto.ca
http://www.alanjacksonastronomy.com/

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Further Information

The new work appears in: “Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I/`Oumuamua", A. Jackson, D. Tamayo, N. Hammond, M. Ali-Dib, H. Rein, Monthly Notices of the Royal Astronomical Society (2018), in press (DOI: 10.1093/mnras/sly033).

A copy of the paper is available here.

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Notes for Editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

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Spirals and supernovae

NGC 1015

Credit: ESA/Hubble & NASA, A. Riess (STScl/JHU)

This stunning image from Hubble shows the majestic galaxy NGC 1015, found nestled within the constellation of Cetus (The Whale) 118 million light-years from Earth. In this image, we see NGC 1015 face-on, with its beautifully symmetrical swirling arms and bright central bulge creating a scene akin to a sparkling Catherine wheel firework.

NGC 1015 has a bright, fairly large centre and smooth, tightly wound spiral arms and a central “bar” of gas and stars. This shape leads NGC 1015 to be classified as a barred spiral galaxy — just like our home, the Milky Way. Bars are found in around two-thirds of all spiral galaxies, and the arms of this galaxy swirl outwards from a pale yellow ring encircling the bar itself. Scientists believe that any hungry black holes lurking at the centre of barred spirals funnel gas and energy from the outer arms into the core via these glowing bars, feeding the black hole, fueling star birth at the centre and building up the galaxy’s central bulge.

In 2009, a Type Ia supernova named SN 2009ig was spotted in NGC 1015 — one of the bright dots to the upper right of the galaxy’s centre. These types of supernovae are extremely important: they are all caused by exploding white dwarfs which have companion stars, and always peak at the same brightness — 5 billion times brighter than the Sun. Knowing the true brightness of these events, and comparing this with their apparent brightness, gives astronomers a unique chance to measure distances in the Universe.

Source: ESA/Hubble/Potw

Crab Nebula: A Crab Walks Through Time

 Crab Nebula

Credit  X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

JPEG (391.3 kb) - Large JPEG (4.8 MB) - Tiff (13.1 MB) - More Images

Tour of the Crab Nebula - More Animations

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Next year marks the 20th anniversary of NASA's Chandra X-ray Observatory launch into space. The Crab Nebula was one of the first objects that Chandra examined with its sharp X-ray vision, and it has been a frequent target of the telescope ever since.

There are many reasons that the Crab Nebula is such a well-studied object. For example, it is one of a handful of cases where there is strong historical evidence for when the star exploded. Having this definitive timeline helps astronomers understand the details of the explosion and its aftermath.

In the case of the Crab, observers in several countries reported the appearance of a "new star" in 1054 A.D. in the direction of the constellation Taurus. Much has been learned about the Crab in the centuries since then. Today, astronomers know that the Crab Nebula is powered by a quickly spinning, highly magnetized neutron star called a pulsar, which was formed when a massive star ran out of its nuclear fuel and collapsed. The combination of rapid rotation and a strong magnetic field in the Crab generates an intense electromagnetic field that creates jets of matter and anti-matter moving away from both the north and south poles of the pulsar, and an intense wind flowing out in the equatorial direction.

The latest image of the Crab is a composite with X-rays from Chandra (blue and white), NASA's Hubble Space Telescope (purple) and NASA's Spitzer Space Telescope (pink). The extent of the X-ray image is smaller than the others because extremely energetic electrons emitting X-rays radiate away their energy more quickly than the lower-energy electrons emitting optical and infrared light.

This new composite adds to a scientific legacy, spanning nearly two decades, between Chandra and the Crab Nebula. Here is a sample of the many insights astronomers have gained about this famous object using Chandra and other telescopes.

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1999: Within weeks of being deployed into orbit from the Space Shuttle Columbia during the summer of 1999, Chandra observed the Crab Nebula. The Chandra data revealed features in the Crab never seen before, including a bright ring of high-energy particles around the heart of the nebula.

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2002: The dynamic nature of the Crab Nebula was vividly revealed in 2002 when scientists produced videos based on coordinated Chandra and Hubble observations made over several months. The bright ring seen earlier consists of about two dozen knots that form, brighten and fade, jitter around, and occasionally undergo outbursts that give rise to expanding clouds of particles, but remain in roughly the same location.

These knots are caused by a shock wave, similar to a sonic boom, where fast-moving particles from the pulsar are slamming into surrounding gas. Bright wisps originating in this ring are moving outward at half the speed of light to form a second expanding ring further away from the pulsar.

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2006: In 2003, the Spitzer Space Telescope was launched and the space-based infrared telescope joined Hubble, Chandra, and the Compton Gamma-ray Observatory and completed the development of NASA's "Great Observatory" program. A few years later, the first composite of the Crab with data from Chandra (light blue), Hubble (green and dark blue), and Spitzer (red) was released. 

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2008: As Chandra continued to take observations of the Crab, the data provided a clearer picture of what was happening in this dynamic object. In 2008, scientists first reported a view of the faint boundary of the Crab Nebula's pulsar wind nebula (i.e., a cocoon of high-energy particles surrounding the pulsar).

The data showed structures that astronomers referred to as "fingers", "loops", and "bays". These features indicated that the magnetic field of the nebula and filaments of cooler matter are controlling the motion of the electrons and positrons. The particles can move rapidly along the magnetic field and travel several light years before radiating away their energy. In contrast, they move much more slowly perpendicular to the magnetic field, and travel only a short distance before losing their energy.

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2011: Time-lapse movies of Chandra data of the Crab have been powerful tools in showing the dramatic variations in the X-ray emission near the pulsar. In 2011, Chandra observations, obtained between September 2010 and April 2011, were obtained to pinpoint the location of remarkable gamma-ray flares observed by NASA's Fermi Gamma Ray Observatory and Italy's AGILE Satellite. The gamma-ray observatories were not able to locate the source of the flares within the nebula, but astronomers hoped that Chandra, with its high-resolution images, would.

Two Chandra observations were made when strong gamma-ray flares occurred, but no clear evidence was seen for correlated flares in the Chandra images.

Despite this lack of correlation, the Chandra observations helped scientists to home in on an explanation of the gamma-ray flares. Though other possibilities remain, Chandra provided evidence that accelerated particles produced the gamma-ray flares.

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2014: To celebrate the 15th anniversary of Chandra's launch, several new images of supernova remnants were released, including the Crab Nebula. This was a "three color" image of the Crab Nebula, where the X-ray data were split into three different energy bands. In this image, the lowest-energy X-rays Chandra detects are red, the medium range are green, and the highest-energy X-rays from the Crab are colored blue. Note that the extent of the higher energy X-rays in the image is smaller than the others. This is because the most energetic electrons responsible for the highest energy X-rays radiate away their energy more quickly than the lower-energy electrons.

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2017: Building on the multiwavelength images of the Crab from the past, a highly detailed view of the Crab Nebula was created in 2017 using data from telescopes spanning nearly the entire breadth of the electromagnetic spectrum. Radio waves from the Karl G. Jansky Very Large Array (red), Hubble optical data (green), infrared data from Spitzer (yellow), and X-ray data from XMM-Newton (blue) and Chandra (purple) produced a spectacular new image of the Crab.

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NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

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Fast Facts for Crab Nebula:

Scale: Image is about 5 arcmin (10 light years) across
Category: Supernovas & Supernova Remnants, Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 05h 34m 32s | Dec +22° 0.0' 52.00"
Constellation: Taurus
Observation Date: 48 pointings between March 2000 and Nov 2013
Observation Time: 25 hours 28 min (1 day 1 hour 28 min)

Obs. ID 769-773, 1994-2001, 4607, 13139, 13146, 13147, 13150-13154, 13204-13210, 13750-13752, 13754-13757, 14416, 14458, 14678-14682, 14685, 16245, 16257, 16357, 16358

Instrument: ACIS
Also Known As: NGC 1952
Color Code: X-ray (Blue), Optical (Purple), Infrared (Pink)

Source: NASA’s Chandra X-ray Observatory

Stephen Hawking, 8 January 1942 – 14 March 2018

 Stephen Hawking (1942-2018)

On 14th January 2018 Professor Stephen Hawking died peacefully at his home in Cambridge at the age of 76.

Stephen Hawking is widely recognised as one of the most influential theoretical physicists in modern times. He has made seminal contributions to several areas of astrophysics. In particular, his studies have provided some of the pillars of our understanding of black holes, including the concept that black holes must have a temperature and must generate radiation (known as Hawking radiation). More broadly, his studies have resulted in major fundamental advances in areas of cosmology and general relativity.

He was the Lucasian Professor of Mathematics at the University of Cambridge (the same chair held by Isaac Newton) from 1979 to 2009. In 2007 he founded the Centre for Theoretical Cosmology, of which he was Director of Research until 2014 and then he was the Dennis Stanton Avery and Sally Tsui Wong-Avery Director of Research. He received many awards and honours, including the Hughes and Copley Medals of the Royal Society, the US Presidential Medal of Freedom, and the Fundamental Physics prize.

Stephen Hawking wrote milestone research papers and well known scientific books. He also wrote several popular science books, such as the famous "A Brief History of Time".

Within the context of the Kavli Institute, Stephen supported the creation of the Institute and most recently has helped us to expand our research in Gravitational Waves, an area in which he has been a pioneer.

Stephen was a source of inspiration for all of us and we will greatly miss him.

Stephen Hawking (centre), together with Roberto Maiolino (Director of the Kavli Institute, left) and members of the Kavli Foundation Board of Directors and Staff during their visit in November 2017.

Source:  Kavli Institute for Cosmology, Cambridge/News

Jupiter's Great Red Spot Getting Taller as it Shrinks, NASA Team Finds

This extract from a global map of Jupiter was made from observations performed with NASA’s Hubble Space Telescope.  

Credit: NASA's Goddard Space Flight Center

Scientists have noticed that Jupiter's Great Red Spot has been getting smaller over time. Now, there's evidence the storm is actually growing taller as it shrinks. Credits: NASA's Goddard Space Flight Center. This video is public domain and can be downloaded from NASA's Scientific Visualization Studio.

Though once big enough to swallow three Earths with room to spare, Jupiter’s Great Red Spot has been shrinking for a century and a half. Nobody is sure how long the storm will continue to contract or whether it will disappear altogether.

A new study suggests that it hasn’t all been downhill, though. The storm seems to have increased in area at least once along the way, and it’s growing taller as it gets smaller.

“Storms are dynamic, and that’s what we see with the Great Red Spot. It’s constantly changing in size and shape, and its winds shift, as well,” said Amy Simon, an expert in planetary atmospheres at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new paper, published in the Astronomical Journal.

Observations of Jupiter date back centuries, but the first confirmed sighting of the Great Red Spot was in 1831. (Researchers aren’t certain whether earlier observers who saw a red spot on Jupiter were looking at the same storm.)

Keen observers have long been able to measure the size and drift of the Great Red Spot by fitting their telescopes with an eyepiece scored with crosshairs. A continuous record of at least one observation of this kind per year dates back to 1878.

Simon and her colleagues drew on this rich archive of historical observations and combined them with data from NASA spacecraft, starting with the two Voyager missions in 1979. In particular, the group relied on a series of annual observations of Jupiter that team members have been conducting with NASA’s Hubble Space Telescope as part of the Outer Planets Atmospheres Legacy, or OPAL, project. The OPAL team scientists are based at Goddard, the University of California at Berkeley, and NASA’s Jet Propulsion Laboratory in Pasadena, California.

The team traced the evolution of the Great Red Spot, analyzing its size, shape, color  and drift rate. They also looked at the storm’s internal wind speeds, when that information was available from spacecraft.

The new findings indicate that the Great Red Spot recently started to drift westward faster than before. The storm always stays at the same latitude, held there by jet streams to the north and south, but it circles the globe in the opposite direction relative to the planet’s eastward rotation. Historically, it’s been assumed that this drift is more or less constant, but in recent observations, the team found the spot is zooming along much faster.

The study confirms that the storm has been decreasing in length overall since 1878 and is big enough to accommodate just over one Earth at this point. But the historical record indicates the area of the spot grew temporarily in the 1920s.

“There is evidence in the archived observations that the Great Red Spot has grown and shrunk over time,” said co-author Reta Beebe, an emeritus professor at New Mexico State University in Las Cruces. “However, the storm is quite small now, and it’s been a long time since it last grew.”

Because the storm has been contracting, the researchers expected to find the already-powerful internal winds becoming even stronger, like an ice skater who spins faster as she pulls in her arms.

Instead of spinning faster, the storm appears to be forced to stretch up. It’s almost like clay being shaped on a potter’s wheel. As the wheel spins, an artist can transform a short, round lump into a tall, thin vase by pushing inward with his hands. The smaller he makes the base, the taller the vessel will grow.

In the case of the Great Red Spot, the change in height is small relative to the area that the storm covers, but it’s still noticeable.

The Great Red Spot’s color has been deepening, too, becoming intensely orange since 2014. Researchers aren’t sure why that’s happening, but it’s possible that the chemicals which color the storm are being carried higher into the atmosphere as the spot stretches up. At higher altitudes, the chemicals would be subjected to more UV radiation and would take on a deeper color.

In some ways, the mystery of the Great Red Spot only seems to deepen as the iconic storm contracts. Researchers don’t know whether the spot will shrink a bit more and then stabilize, or break apart completely.

“If the trends we see in the Great Red Spot continue, the next five to 10 years could be very interesting from a dynamical point of view,” said Goddard co-author Rick Cosentino. “We could see rapid changes in the storm’s physical appearance and behavior, and maybe the red spot will end up being not so great after all.”

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By Elizabeth Zubritsky
NASA’s Goddard Space Flight Center in Greenbelt, Md.

Editor: Karl Hille

Source: NASA/Jupiter