Wednesday, July 17, 2019

Lunar Reconnaissance Orbiter Camera Simulates View from Lunar Module

The only visual record of the historic Apollo 11 landing is from a 16mm time-lapse (6 frames per second) movie camera mounted in Buzz Aldrin’s window (right side of Lunar Module Eagle or LM). 

In this image, the Lunar Module descent stage and astronaut tracks are clearly visible — something Armstrong did not see during the landing. The incidence (solar) angle on the Narrow Angle Camera image is within a degree as when Apollo 11 landed (just after sunrise), so you see the same dramatic shadows. Credits: NASA/Goddard/Arizona State University. Hi-res Image

Due to the small size of the LM windows and the angle at which the movie camera was mounted, what mission commander Neil Armstrong saw as he flew and landed the LM was not recorded. The Lunar Reconnaissance Orbiter Camera (LROC) team reconstructed the last three minutes of the landing trajectory (latitude, longitude, orientation, velocity, altitude) using landmark navigation and altitude call outs from the voice recording. From this trajectory information, and high resolution LROC Narrow Angle Camera (LROC NAC) images and topography, we simulated what Armstrong saw in those final minutes as he guided the LM down to the surface of the Moon. As the video begins, Armstrong could see the aim point was on the rocky northeastern flank of West crater (190 meters diameter), causing him to take manual control and fly horizontally, searching for a safe landing spot. At the time, only Armstrong saw the hazard; he was too busy flying the LM to discuss the situation with mission control.

After flying over the hazards presented by the bouldery flank of West crater, Armstrong spotted a safe spot about 500 meters down track where he carefully descended to the surface. Just before landing, the LM flew over what would later be called Little West crater (40 meters diameter). Armstrong would visit and photograph this crater during his extra-vehicular activity (EVA). Of course, during the landing, Armstrong was able to lean forward and back and turn his head to gain a view that was better than the simple, fixed viewpoint presented here. However, this simulated movie lets you relive those dramatic moments.

How accurate is our simulated view? We reconstructed the view from Aldrin's window from our derived trajectory, and you can view it side-by-side with the original 16mm film. You be the judge!
This video compares film from the landing of Apollo 11 (left) with a simulated reconstruction (right) based on data from NASA's Lunar Reconnaissance Orbiter. Credits: NASA/Goddard Space Flight Center/Arizona State University
Acknowledgement: A time-synchronized version of the original 16mm film (Apollo Flight Journal) and the First Men on the Moon website, which synchronizes the air-to-ground voice transmission with the original 16mm film, greatly aided the production of this work. These sources were played side-by-side with our reconstruction during its production, allowing us to better match the reconstruction to the 16mm film and altitude callouts.

Image credits: NASA/Goddard Space Flight Center/Arizona State University

Editor: Karl Hille

Tuesday, July 16, 2019

New Hubble Constant Measurement Adds to Mystery of Universe's Expansion Rate

Galaxies Used to Refine the Hubble Constant
Credit: NASA, ESA, W. Freedman (University of Chicago), ESO, and the Digitized Sky Survey

Astronomers have made a new measurement of how fast the universe is expanding, using an entirely different kind of star than previous endeavors. The revised measurement, which comes from NASA's Hubble Space Telescope, falls in the center of a hotly debated question in astrophysics that may lead to a new interpretation of the universe's fundamental properties.

Scientists have known for almost a century that the universe is expanding, meaning the distance between galaxies across the universe is becoming ever more vast every second. But exactly how fast space is stretching, a value known as the Hubble constant, has remained stubbornly elusive.

Now, University of Chicago professor Wendy Freedman and colleagues have a new measurement for the rate of expansion in the modern universe, suggesting the space between galaxies is stretching faster than scientists would expect. Freedman's is one of several recent studies that point to a nagging discrepancy between modern expansion measurements and predictions based on the universe as it was more than 13 billion years ago, as measured by the European Space Agency's Planck satellite.

As more research points to a discrepancy between predictions and observations, scientists are considering whether they may need to come up with a new model for the underlying physics of the universe in order to explain it. 

"The Hubble constant is the cosmological parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves," said Freedman. "The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an immediate and compelling reason to believe that there is something fundamentally flawed in our current model of the universe.”

In a new paper accepted for publication in The Astrophysical Journal, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their new observations, made using Hubble, indicate that the expansion rate for the nearby universe is just under 70 kilometers per second per megaparsec (km/sec/Mpc). One parsec is equivalent to 3.26 light-years distance.

This measurement is slightly smaller than the value of 74 km/sec/Mpc recently reported by the Hubble SH0ES (Supernovae H0 for the Equation of State) team using Cepheid variables, which are stars that pulse at regular intervals that correspond to their peak brightness. This team, led by Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Baltimore, Maryland, recently reported refining their observations to the highest precision to date for their Cepheid distance measurement technique.

How to Measure Expansion

A central challenge in measuring the universe's expansion rate is that it is very difficult to accurately calculate distances to distant objects.

In 2001, Freedman led a team that used distant stars to make a landmark measurement of the Hubble constant. The Hubble Space Telescope Key Project team measured the value using Cepheid variables as distance markers. Their program concluded that the value of the Hubble constant for our universe was 72 km/sec/Mpc.

But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the big bang, which is called the Cosmic Microwave Background. The Planck measurements allow scientists to predict how the early universe would likely have evolved into the expansion rate astronomers can measure today. Scientists calculated a value of 67.4 km/sec/Mpc, in significant disagreement with the rate of 74.0 km/sec/Mpc measured with Cepheid stars.

Astronomers have looked for anything that might be causing the mismatch. "Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don't yet understand about the stars we're measuring, or whether our cosmological model of the universe is still incomplete," Freedman said. "Or maybe both need to be improved upon."

Freedman's team sought to check their results by establishing a new and entirely independent path to the Hubble constant using an entirely different kind of star.

Certain stars end their lives as a very luminous kind of star called a red giant, a stage of evolution that our own Sun will experience billions of years from now. At a certain point, the star undergoes a catastrophic event called a helium flash, in which the temperature rises to about 100 million degrees and the structure of the star is rearranged, which ultimately dramatically decreases its luminosity. 

Astronomers can measure the apparent brightness of the red giant stars at this stage in different galaxies, and they can use this as a way to tell their distance.

The Hubble constant is calculated by comparing distance values to the apparent recessional velocity of the target galaxies — that is, how fast galaxies seem to be moving away. The team's calculations give a Hubble constant of 69.8 km/sec/Mpc — straddling the values derived by the Planck and Riess teams.

"Our initial thought was that if there's a problem to be resolved between the Cepheids and the Cosmic Microwave Background, then the red giant method can be the tie-breaker," said Freedman.

But the results do not appear to strongly favor one answer over the other say the researchers, although they align more closely with the Planck results.

NASA's upcoming mission, the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s, will enable astronomers to better explore the value of the Hubble constant across cosmic time. WFIRST, with its Hubble-like resolution and 100 times greater view of the sky, will provide a wealth of new Type Ia supernovae, Cepheid variables, and red giant stars to fundamentally improve distance measurements to galaxies near and far.

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.


Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Louise Lerner
University of Chicago, Chicago, Illinois

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Friday, July 12, 2019

‘Moon-forming’ Circumplanetary Disk Discovered in Distant Star System

Artist impression of the circumplanetary disk recently discovered around a young planet in the PDS 70 star system. Credit: NRAO/AUI/NSF, S. Dagnello. Hi-Res File

ALMA image of the dust in PDS 70, a star system located approximately 370 light-years from Earth. Two faint smudges in the gap region of this disk are associated with newly formed planets. One such concentration of dust is a circumplanetary disk, the first such feature ever detected around a distant star. Credit: ALMA (ESO/NAOJ/NRAO); A. Isella. Hi-Res File

Composite image of PDS 70. Comparing new ALMA data to earlier VLT observations, astronomers determined that the young planet designated PDS 70 c has a circumplanetary disk, a feature that is strongly theorized to be the birthplace of moons. Credit: ALMA (ESO/NAOJ/NRAO) A. Isella; ESO. Hi-Res File

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the first-ever observations of a circumplanetary disk, the planet-girding belt of dust and gas that astronomers strongly theorize controls the formation of planets and gives rise to an entire system of moons, like those found around Jupiter.

Atacama Large Millimeter/submillimeter Array (ALMA)Funded by the U.S. National Science Foundation and its international partners (NRAO/ESO/NAOJ), ALMA is among the most complex and powerful astronomical observatories on Earth or in space. The telescope is an array of 66 high-precision dish antennas in northern Chile.

This never-before-seen feature was discovered around one of the planets in PDS 70, a young star located approximately 370 light-years from Earth. Recently, astronomers confirmed the presence of two massive, Jupiter-like planets there. This earlier discovery was made with the European Southern Observatory’s Very Large Telescope (VLT), which detected the warm glow naturally emitted by hydrogen gas accreting onto the planets.

The new ALMA observations instead image the faint radio waves given off by the tiny (about one tenth of a millimeter across) particles of dust around the star.

The ALMA data, combined with the earlier optical and infrared VLT observations, provide compelling evidence that a dusty disk capable of forming multiple moons surrounds the outermost known planet in the system.

“For the first time, we can conclusively see the telltale signs of a circumplanetary disk, which helps to support many of the current theories of planet formation,” said Andrea Isella, an astronomer at Rice University in Houston, Texas, and lead author on a paper published in the Astrophysical Journal, Letters.

“By comparing our observations to the high-resolution infrared and optical images, we can clearly see that an otherwise enigmatic concentration of tiny dust particles is actually a planet-girding disk of dust, the first such feature ever conclusively observed,” he said. According to the researchers, this also is the first time that a planet has been clearly seen in these three distinct bands of light.

Unlike the icy rings of Saturn, which likely formed by the crashing together of comets and rocky bodies relatively recently in the history of our solar system, a circumplanetary disk is the lingering remains of the planet-formation process.

The ALMA data also revealed two distinct differences between the two newly discovered planets. The closer in of the two, PDS 70 b, which is about the same distance from its star as Uranus is from the Sun, has a trailing mass of dust behind it resembling a tail. “What this is and what it means for this planetary system is not yet known,” said Isella. “The only conclusive thing we can say is that it is far enough from the planet to be an independent feature.”

The second planet, PDS 70 c, resides in the exact same location as a clear knot of dust seen in the ALMA data. Since this planet is shining so brightly in the infrared and hydrogen bands of light, the astronomers can convincingly say that a fully formed planet is already in orbit there and that nearby gas continues to be syphoned onto the planet’s surface, finishing its adolescent growth spurt.

This outer planet is located approximately 5.3 billion kilometers from the host star, about the same distance as Neptune from our Sun. Astronomers estimate that this planet is approximately 1 to 10 times the mass of Jupiter. “If the planet is on the larger end of that estimate, it’s quite possible there might be planet-size moons in formation around it,” noted Isella.

The ALMA data also add one more important element to these observations.

Optical studies of planetary systems are notoriously challenging. Since the star is so much brighter than the planets, it is difficult to filter out the glare, much like trying to spot a firefly next to a search light. ALMA observations, however, don’t have that limitation since stars emit comparatively little light at millimeter and submillimeter wavelengths.

“This means we’ll be able to come back to this system at different time periods and more easily map the orbit of the planets and the concentration of dust in the system,” concluded Isella. “This will give us unique insights into the orbital properties of solar systems in their very earliest stages of development.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


Charles E. Blue: Public Information Officer;


“Detection of continuum submillimeter emission associated with candidate protoplanets,” A. Isella, et al., the Astrophysical Journal Letters:; Preprint:

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Thursday, July 11, 2019

Hubble Discovers Mysterious Black Hole Disc

 PR Image heic1913a
Artist’s impression of NGC3147 black hole disc 
Top-Down view of artist’s impression of NGC3147 black hole disc

PR Image heic1913c
Galaxy NGC 3147 


Artist’s Impression of NGC3147 black hole disc
Artist’s Impression of NGC3147 black hole disc

Top-Down View of Artist’s Impression of NGC3147 black hole disc
Top-Down View of Artist’s Impression of NGC3147 black hole disc

Astronomers using the NASA/ESA Hubble Space Telescope have observed an unexpected thin disc of material encircling a supermassive black hole at the heart of the spiral galaxy NGC 3147, located 130 million light-years away.

The presence of the black hole disc in such a low-luminosity active galaxy has astronomers surprised. Black holes in certain types of galaxies such as NGC 3147 are considered to be starving as there is insufficient gravitationally captured material to feed them regularly. It is therefore puzzling that there is a thin disc encircling a starving black hole that mimics the much larger discs found in extremely active galaxies. 

Of particular interest, this disc of material circling the black hole offers a unique opportunity to test Albert Einstein’s theories of relativity. The disc is so deeply embedded in the black hole’s intense gravitational field that the light from the gas disc is altered, according to these theories, giving astronomers a unique peek at the dynamic processes close to a black hole. 

We’ve never seen the effects of both general and special relativity in visible light with this much clarity,” said team member Marco Chiaberge of AURA for ESA, STScI and Johns Hopkins Univeristy.

The disc’s material was measured by Hubble to be whirling around the black hole at more than 10% of the speed of light. At such extreme velocities, the gas appears to brighten as it travels toward Earth on one side, and dims as it speeds away from our planet on the other. This effect is known as relativistic beaming. Hubble’s observations also show that the gas is embedded so deep in a gravitational well that light is struggling to escape, and therefore appears stretched to redder wavelengths. The black hole’s mass is around 250 million times that of the Sun. 

This is an intriguing peek at a disc very close to a black hole, so close that the velocities and the intensity of the gravitational pull are affecting how we see the photons of light,” explained the study’s first author, Stefano Bianchi, of Università degli Studi Roma Tre in Italy. 

In order to study the matter swirling deep inside this disc, the researchers used the Hubble Space Telescope Imaging Spectrograph (STIS) instrument. This diagnostic tool divides the light from an object into its many individual wavelengths to determine the object's speed, temperature, and other characteristics at very high precision. STIS was integral to effectively observing the low-luminosity region around the black hole, blocking out the galaxy’s brilliant light. 

The astronomers initially selected this galaxy to validate accepted models about lower-luminosity active galaxies: those with malnourished black holes. These models predict that discs of material should form when ample amounts of gas are trapped by a black hole’s strong gravitational pull, subsequently emitting lots of light and producing a brilliant beacon called a quasar

The type of disc we see is a scaled-down quasar that we did not expect to exist,” Bianchi explained. “It’s the same type of disc we see in objects that are 1000 or even 100 000 times more luminous. The predictions of current models for very faint active galaxies clearly failed.

The team hopes to use Hubble to hunt for other very compact discs around low-luminosity black holes in similar active galaxies.

More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The team’s paper will appear in the journal the Monthly Notices of the Royal Astronomical Society.

The international team of astronomers in this study consists of Stefano Bianchi (Universita` degli Studi Roma Tre, Italy), Robert Antonucci (University of California, Santa Barbara, USA), Alessandro Capetti (INAF - Osservatorio Astrofisico di Torino, Italy), Marco Chiaberge (Space Telescope Science Institute and Johns Hopkins University, Baltimore, USA), Ari Laor (Israel Institute of Technology, Israel), Loredana Bassani (INAF/IASF Bologna, Italy), Francisco J. Carrera (CSIC-Universidad de Cantabria, Spain), Fabio La Franca (Universita` degli Studi Roma Tre, Italy), Andrea Marinucci (Universita` degli Studi Roma Tre, Italy), Giorgio Matt1 (Universita` degli Studi Roma Tre, Italy), Riccardo Middei (Universita` degli Studi Roma Tre, Italy), Francesca Panessa (INAF Istituto di Astrofisica e Planetologia Spaziali, Italy).

Image credit: ESA/Hubble, M. Kornmesser 



Stefano Bianchi
Dipartimento di Matematica e Fisica, Universita` degli Studi Roma Tre
Rome, Italy

Bethany Downer
ESA/Hubble, Public Information Officer
Garching, Germany

Wednesday, July 10, 2019

Star formation may be halted by cold ionised hydrogen

A composite image showing our Galaxy, the Milky Way, rising above the Engineering Development Array at the Murchison Radio-astronomy Observatory in Western Australia. The location of the centre of our Galaxy is highlighted alongside the ionized hydrogen (H+) signal detected from this region of sky. The white-blueish light shows the stars making up the Milky Way and the dark patches obscuring this light shows the cold gas that is interspersed between them. Credit: Engineering Development Array image courtesy of ICRAR. Milky Way image courtesy of Sandino Pusta.

For the first time ionised hydrogen has been detected at the lowest frequency ever towards the centre of our Galaxy. The findings originate from a cloud that is both very cold (around -230 degrees Celsius) and also ionised, something that has never been detected before. This discovery may help to explain why stars don’t form as quickly as they theoretically could.

Dr. Raymond Oonk (ASTRON/Leiden Observatory/SURFsara) led this study which is published today in MNRAS. He said: "The possible existence of cold ionised gas had been hinted at in previous work, but this is the first time we clearly see it."

Ionisation is an energetic process that strips electrons away from atoms. The atom will become electrically charged and can then be called an ion. This typically happens in gas that is very hot (10000 degrees Celsius) and where atoms can easily lose their electrons. It was therefore puzzling to discover the ionised hydrogen from very cold gas in this cloud. Normal energy sources, such as photons from massive stars, would not cause this. More exotic energy forms, such as high energy particles created in supernova shockwaves and near black holes, are more likely to be responsible.

Dr. Oonk continues: "This discovery shows that the energy needed to ionise hydrogen atoms can penetrate deep into cold clouds. Such cold clouds are believed to be the fuel from which new stars are born. However, in our Galaxy we know that the stellar birth rate is very low, much lower than naively expected. Perhaps the energy observed here acts as a stabiliser for cold clouds, thereby preventing them from collapsing on to themselves and forming new stars."

The observation was made with the Engineering Development Array (EDA), a prototype station of the Square Kilometre Array (SKA), the worlds’ largest radio telescope. A/Prof. Randall Wayth (Curtin University/ICRAR) says: "This detection was made possible by the wide bandwidth of the EDA and the extremely radio quiet location of the Murchison Radio-astronomy Observatory. The low frequency portion of the Square Kilometre Array will be built at this location in the coming years, so this excellent result gives us a glimpse of what the SKA will be capable of once it's built."

The data reduction was led by Emma Alexander (University of Manchester) as part of her summer student internship at ASTRON: "It’s a very exciting time to be coming into radio astronomy, and it was great to work on the first high resolution spectroscopic data from this SKA prototype station. The technologies that are being developed for the SKA, and the science results that come from them, will be a driving force for my generation of radio astronomers."

This work was carried out as a collaboration between the Netherlands Institute for Radio Astronomy (ASTRON), Leiden University, the International Centre for Radio Astronomy Research (ICRAR), University of Manchester and the Square Kilometre Array.

Tuesday, July 09, 2019

New Method May Resolve Difficulty in Measuring Universe’s Expansion

Artist's impression of the explosion and burst of gravitational waves emitted when a pair of superdense neutron stars collide. New observations with radio telescopes show that such events can be used to measure the expansion rate of the Universe. Credit: NRAO/AUI/NSF. Hi-Res File

Radio observations of a jet of material ejected in the aftermath of the neutron-star merger were key to allowing astronomers to determine the orientation of the orbital plane of the stars prior to their merger, and thus the "brightness" of the gravitational waves emitted in the direction of Earth. This can make such events an important new tool for measuring the expansion rate of the Universe. Credit: Sophia Dagnello, NRAO/AUI/NSF. Hi-Res File

Astronomers using National Science Foundation (NSF) radio telescopes have demonstrated how a combination of gravitational-wave and radio observations, along with theoretical modeling, can turn the mergers of pairs of neutron stars into a “cosmic ruler” capable of measuring the expansion of the Universe and resolving an outstanding question over its rate.

The astronomers used the NSF’s Very Long Baseline Array (VLBA), the Karl G. Jansky Very Large Array (VLA) and the Robert C. Byrd Green Bank Telescope (GBT) to study the aftermath of the collision of two neutron stars that produced gravitational waves detected in 2017. This event offered a new way to measure the expansion rate of the Universe, known by scientists as the Hubble Constant. The expansion rate of the Universe can be used to determine its size and age, as well as serve as an essential tool for interpreting observations of objects elsewhere in the Universe.

Two leading methods of determining the Hubble Constant use the characteristics of the Cosmic Microwave Background, the leftover radiation from the Big Bang, or a specific type of supernova explosions, called Type Ia, in the distant Universe. However, these two methods give different results.

“The neutron star merger gives us a new way of measuring the Hubble Constant, and hopefully of resolving the problem,” said Kunal Mooley, of the National Radio Astronomy Observatory (NRAO) and Caltech.

The technique is similar to that using the supernova explosions. Type Ia supernova explosions are thought to all have an intrinsic brightness which can be calculated based on the speed at which they brighten and then fade away. Measuring the brightness as seen from Earth then tells the distance to the supernova explosion. Measuring the Doppler shift of the light from the supernova’s host galaxy indicates the speed at which the galaxy is receding from Earth. The speed divided by the distance yields the Hubble Constant. To get an accurate figure, many such measurements must be made at different distances.

When two massive neutron stars collide, they produce an explosion and a burst of gravitational waves. The shape of the gravitational-wave signal tells scientists how “bright” that burst of gravitational waves was. Measuring the “brightness,” or intensity of the gravitational waves as received at Earth can yield the distance.

“This is a completely independent means of measurement that we hope can clarify what the true value of the Hubble Constant is,” Mooley said.

However, there’s a twist. The intensity of the gravitational waves varies with their orientation with respect to the orbital plane of the two neutron stars. The gravitational waves are stronger in the direction perpendicular to the orbital plane, and weaker if the orbital plane is edge-on as seen from Earth.

“In order to use the gravitational waves to measure the distance, we needed to know that orientation,” said Adam Deller, of Swinburne University of Technology in Australia.

Over a period of months, the astronomers used the radio telescopes to measure the movement of a superfast jet of material ejected from the explosion. “We used these measurements along with detailed hydrodynamical simulations to determine the orientation angle, thus allowing use of the gravitational waves to determine the distance,” said Ehud Nakar from Tel Aviv University.

This single measurement, of an event some 130 million light-years from Earth, is not yet sufficient to resolve the uncertainty, the scientists said, but the technique now can be applied to future neutron-star mergers detected with gravitational waves.

“We think that 15 more such events that can be observed both with gravitational waves and in great detail with radio telescopes, may be able to solve the problem,” said Kenta Hotokezaka, of Princeton University. “This would be an important advance in our understanding of one of the most important aspects of the Universe,” he added.

The international scientific team led by Hotokezaka is reporting its results in the journal Nature Astronomy.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

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Monday, July 08, 2019

Powering the Extreme Jets of Active Galaxies

Black-hole-powered galaxies called blazars have powerful jets that are thought to be fortuitously aimed directly toward Earth. Astronomers have used multi-band observations, from the gamma-ray to the radio, to study the powerful jets and their driving sources. Credit: NASA; M. Weiss/CfA

An active galaxy nucleus (AGN) contains a supermassive black hole that is vigorously accreting material. It typically ejects jets of particles that move at close to the speed of light, radiating across many wavelengths, in particular the X-ray, in processes are among the most energetic phenomena in the universe. The jets are often also highly collimated and extend far beyond their host galaxy, and if they happen to be pointed along our line of sight they are the most spectacular class of this phenomenon: blazars.

A few years ago astronomers noticed that some types of blazars have jet powers that appear to exceed the power provided by the accretion. Two ideas were put forward to explain the difference: the jets are also extracting power from the spin of the black hole or from the magnetic flux around the object. How either process happens – if indeed they do happen - is hotly debated, but one popular line of argument asserts that the processes are somehow related to the mass of the supermassive black hole, with the most massive cases (more than a hundred million solar-masses) being the most anomalous. Recently the Fermi Gamma-Ray Space Telescope detected gamma-rays (even more energetic photons than X-rays) coming from jets in a class of galaxies called Seyferts, spiral galaxies with relatively small supermassive black hole masses, typically about ten million solar-masses. Astronomers speculated that these relatively low-mass yet powerful emission engines might provide keys to sorting out the various sources of jet power.

CfA astronomer Mislav Balokovic and his colleagues completed a multi-wavelength study of the bright blazar-like Seyfert galaxy PKSJ1222+0413 and included data from the gamma-ray to the radio, both archival and new observations, including new results from the NuSTAR space observatory They then undertook a complete modeling of this source, the most distant one of its type known - its light has been traveling towards us for about eight billion years. They detected the pronounced signature of an accretion disk, and estimated the mass of the supermassive black hole from the widths and strengths of the emission lines to be about two hundred million solar-masses, about ten times higher than most other Seyferts of its type. The jet luminosity is only about half the accretion luminosity, unlike cases like galaxies whose jet power exceeds the accretion. But the object nonetheless clearly falls into a transition regime for jet strengths, enabling future studies to study in more detail the origins of jet power both Seyfert galaxies and in blazars.


"The Relativistic Jet of the γ-ray Emitting Narrow-Line Seyfert 1 Galaxy PKS J1222+0413," Daniel Kynoch, Hermine Landt, Martin J. Ward, Chris Done, Catherine Boisson, Mislav Balokovic, Emmanouil Angelakis, and Ioannis Myserlis, MNRAS 487, 181, 2019.

Friday, July 05, 2019

X-rays Spot Spinning Black Holes Across Cosmic Sea

Credit:  NASA/CXC/Univ. of Oklahoma/X. Dai et al.

Like whirlpools in the ocean, spinning black holes in space create a swirling torrent around them. However, black holes do not create eddies of wind or water. Rather, they generate disks of gas and dust heated to hundreds of millions of degrees that glow in X-ray light.

Using data from NASA's Chandra X-ray Observatory and chance alignments across billions of light years, astronomers have deployed a new technique to measure the spin of five supermassive black holes. The matter in one of these cosmic vortices is swirling around its black hole at greater than about 70% of the speed of light. 

The astronomers took advantage of a natural phenomenon called a gravitational lens. With just the right alignment, the bending of space-time by a massive object, such as a large galaxy, can magnify and produce multiple images of a distant object, as predicted by Einstein.

In this latest research, astronomers used Chandra and gravitational lensing to study five quasars, each consisting of a supermassive black hole rapidly consuming matter from a surrounding accretion disk. Gravitational lensing of the light from each of these quasars by an intervening galaxy has created multiple images of each quasar, as shown by these Chandra images of four of the targets. The sharp imaging ability of Chandra is needed to separate the multiple, lensed images of each quasar.

The key advance made by researchers in this study was that they took advantage of "microlensing," where individual stars in the intervening, lensing galaxy provided additional magnification of the light from the quasar. A higher magnification means a smaller region is producing the X-ray emission.

The researchers then used the property that a spinning black hole is dragging space around with it and allows matter to orbit closer to the black hole than is possible for a non-spinning black hole. Therefore, a smaller emitting region corresponding to a tight orbit generally implies a more rapidly spinning black hole. The authors concluded from their microlensing analysis that the X-rays come from such a small region that the black holes must be spinning rapidly. 

The results showed that one of the black holes, in the lensed quasar called the "Einstein Cross," (labeled Q2237 in the image above) is spinning at, or almost at, the maximum rate possible. This corresponds to the event horizon, the black hole's point of no return, spinning at the speed of light, which is about 670 million miles per hour. Four other black holes in the sample are spinning, on average, at about half this maximum rate. 

For the Einstein Cross the X-ray emission is from a part of the disk that is less than about 2.5 times the size of the event horizon, and for the other 4 quasars the X-rays come from a region four to five times the size of the event horizon.

How can these black holes spin so quickly? The researchers think that these supermassive black holes likely grew by accumulating most of their material over billions of years from an accretion disk spinning with a similar orientation and direction of spin, rather than from random directions. Like a merry-go-round that keeps getting pushed in the same direction, the black holes kept picking up speed. 

The X-rays detected by Chandra are produced when the accretion disk surrounding the black hole creates a multimillion-degree cloud, or corona above the disk near the black hole. X-rays from this corona reflect off the inner edge of the accretion disk, and the strong gravitational forces near the black hole distort the reflected X-ray spectrum, that is, the amount of X-rays seen at different energies. The large distortions seen in the X-ray spectra of the quasars studied here imply that the inner edge of the disk must be close to the black holes, giving further evidence that they must be spinning rapidly.

The quasars are located at distances ranging from 9.8 billion to 10.9 billion light years from Earth, and the black holes have masses between 160 and 500 million times that of the sun. These observations were the longest ever made with Chandra of gravitationally lensed quasars, with total exposure times ranging between 1.7 and 5.4 days.

A paper describing these results is published in the July 2nd issue of The Astrophysical Journal, and is available online. The authors are Xinyu Dai, Shaun Steele and Eduardo Guerras from the University of Oklahoma in Norman, Oklahoma, Christopher Morgan from the United States Naval Academy in Annapolis, Maryland, and Bin Chen from Florida State University in Tallahassee, Florida.

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.

Source: NASA’s Chandra X-ray Observatory

Fast Facts for Q2237+0305:

Scale: Image is 18 arcsec across. (About 500,000 light years)
Category: Quasars & Active Galaxies
Coordinates (J2000): RA 22h 40m 30.34s | Dec 03° 21´ 28.8"
Constellation: Pegasus
Observation Dates: 20 pointings from Dec 31, 2009 to Jun 6, 2014
Observation Time: 130 hours
Obs. IDs: 11534-11539, 13191, 13195, 12831-12832, 13960-13961, 14513-14518, 16316-16317
Instrument: ACIS
References: Dai, X. et al. 2019, AJ, 879, 35 arXiv:1901.06007
Color Code: X-ray intensity: purple
Distance Estimate: About 9.8 billion light years (z=1.69)

Thursday, July 04, 2019

Fast Radio Burst Pinpointed to Distant Galaxy

Owens Valley Radio Observatory, together with w. m. keck observatory, is providing new clues in an ongoing cosmic mystery. Credit: Caltech/Ovro/G. Hallinan

Maunakea, Hawaii – Fast radio bursts (FRBs) are among the most enigmatic and powerful events in the cosmos. Around 80 of these events—intensely bright millisecond-long bursts of radio waves coming from beyond our galaxy—have been witnessed so far but their causes remain unknown.
In a rare feat, researchers at Caltech’s Owens Valley Radio Observatory (OVRO) have now caught a new burst, called FRB 190523, and, together with the W. M. Keck Observatory in Hawaii, have pinpointed its origins to a galaxy 7.9 billion light-years away. Identifying the galaxies from which these radio bursts erupt is a critical step toward solving the mystery of what triggers them.

Finding the host galaxies of FRBs is not easy. Before this new discovery, only one other burst, called FRB 121102, had been localized to a host galaxy. FRB 121102 was reported in 2014 and then later, in 2017, was pinpointed to a galaxy lying 3 billion light-years away. Recently, a second localized FRB was announced on June 27, 2019. Called FRB 180924, this burst was discovered by a team using the Australian Square Kilometer Array Pathfinder and traced to a galaxy about 4 billion light-years away.
FRB 121102 was easiest to find because it continues to burst every few weeks. Most FRBs, however—including the Australian and OVRO finds—just go off once, making the job of finding their host galaxies harder.

“Finding the locations of the one-off FRBs is challenging because it requires a radio telescope that can both discover these extremely short events and locate them with the resolving power of a mile-wide radio dish,” says Vikram Ravi, a new assistant professor of astronomy at Caltech who works with the radio telescopes at OVRO, which is situated east of the Sierra Nevada mountains in California.

The team then conducted follow-up observations using Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS) to determine the properties of FRB 190523’s host galaxy.

The LRIS data revealed that the host galaxy for FRB 190523 is similar to our Milky Way. This is a surprise because the previously located FRB 121102 originates from a dwarf galaxy that is forming stars more than a hundred times faster than the Milky Way.

“This finding tells us that every galaxy, even a run-of-the-mill galaxy like our Milky Way, can generate an FRB,” says Ravi.

The discovery also suggests that a leading theory for what causes FRBs—the eruption of plasma from young, highly magnetic neutron stars, or magnetars—may need to be rethought.

“The theory that FRBs come from magnetars was developed in part because the earlier FRB 121102 came from an active star-forming environment, where young magnetars can be formed in the supernovae of massive stars,” says Ravi. “But the host galaxy of FRB 190523 is more mellow in comparison. “

The Deep Synoptic Array ten-antenna prototype (DSA-10) searches for fast radio bursts within a sky-area the size of 150 full moons (left). Within this area, the DSA-10 can locate these bursts with immense resolving power, isolating them to regions containing just one galaxy (middle). This feat was achieved for the fast radio burst called FRB 190523, detected by DSA-10 on May 23, 2019. The right panel shows the time profile of the burst above its radio spectrum. Credit: Caltech/OVRO/V. Ravi 

Ultimately, to solve the mystery of FRBs, astronomers hope to uncover more examples of their host galaxies.  

“With the full Deep Synoptic Array, we are going to find and localize FRBs every few days,” says Gregg Hallinan, the director of OVRO and a professor of astronomy at Caltech. “This is an exciting time for FRB discoveries.”

“We’re very excited about the new capabilities to find these enigmatic bursts and we look forward to continuing to provide the critical follow-up data that tell us how distant these objects are and what environments they live in,” says John O’Meara, chief scientist at Keck Observatory.

The researchers also say that FRBs can be used to study the amount and distribution of matter in our universe, which will tell us more about the environments in which galaxies form and evolve. As radio waves from FRBs head toward Earth, intervening matter causes some of the wavelengths to travel faster than others; the wavelengths become dispersed in the same way that a prism spreads apart light into a rainbow. The amount of dispersion tells astronomers exactly how much matter there is between the FRB sources and Earth. 

“Most matter in the universe is diffuse, hot, and outside of galaxies,” says Ravi. “This state of matter, although not ‘dark,’ is difficult to observe directly. However, its effects are clearly imprinted on every FRB, including the one we detected at such a great distance.” 

The Nature study, titled, “A fast radio burst localized to a massive galaxy,” was funded by NSF and Caltech. Other Caltech authors include: Morgan Catha, electronics engineer at OVRO; Larry D’Addario, system engineer; George Djorgovski, professor of astronomy; Richard Hobbs, software developer at OVRO; Jonathon Kocz, digital research engineer; Shri Kulkarni, the George Ellery Hale Professor of Astronomy and Planetary Science; Jun Shi, postdoctoral scholar; Harish Vedantham, a former postdoctoral scholar now at ASTRON, the Netherlands Institute for Radio Astronomy; Sandy Weinreb, visiting associate in astronomy; and David Woody, assistant director of OVRO.

About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a very versatile visible-wavelength imaging and spectroscopy instrument commissioned in 1993 and operating at the Cassegrain focus of Keck I. Since it has been commissioned it has seen two major upgrades to further enhance its capabilities: addition of a second, blue arm optimized for shorter wavelengths of light; and the installation of detectors that are much more sensitive at the longest (red)wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe.  LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in2011 for research determining that the universe was speeding up in its expansion.

About W.M. Keck Observatory

The W. M. Keck Observatory telescopes are the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes atop 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. The data presented herein were obtained at the W. M. Keck Observatory, which is 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 recognize and acknowledge the very significant cultural role that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Spiraling Filaments Feed Young Galaxies

Artist's impression of a growing galaxy shows gas spiraling in toward the center. new observations from the keck cosmic web imager provide the best evidence yet that cold gas spirals directly into growing galaxies via filamentous structures. much of the gas ends up being converted into stars. Image credit: Adam Makarenko/W. M. Keck Observatory

New data from W. M. Keck Observatory show gas directly spiraling into growing galaxies 

Maunakea, Hawaii – Galaxies grow by accumulating gas from their surroundings and converting it to stars, but the details of this process have remained murky. New observations, made using the Keck Cosmic Web Imager (KCWI) at W. M. Keck Observatory in Hawaii, now provide the clearest, most direct evidence yet that filaments of cool gas spiral into young galaxies, supplying the fuel for stars.

“For the first time, we are seeing filaments of gas directly spiral into a galaxy. It’s like a pipeline going straight in,” says Christopher Martin, a professor of physics at Caltech and lead author of a new paper appearing in the July 1 issue of the journal Nature Astronomy. “This pipeline of gas sustains star formation, explaining how galaxies can make stars on very fast timescales.”

For years, astronomers have debated exactly how gas makes its way to the center of galaxies. Does it heat up dramatically as it collides with the surrounding hot gas? Or does it stream in along thin dense filaments, remaining relatively cold? 

“Modern theory suggests that the answer is probably a mix of both, but proving the existence of these cold streams of gas had remained a major challenge until now,” says co-author Donal O’Sullivan (MS ’15), a PhD student in Martin’s group who built part of KCWI.

KCWI, designed and built at Caltech, is a state-of-the-art spectral imaging camera. Called an integral-field unit spectrograph, it allows astronomers to take images such that every pixel in the image contains a dispersed spectrum of light. Installed at Keck Observatory in early 2017, KCWI is the successor to the Cosmic Web Imager (CWI), an instrument that has operated at Palomar Observatory near San Diego since 2010. KCWI has eight times the spatial resolution and 10 times the sensitivity of CWI. 

“The main driver for building KCWI was understanding and characterizing the cosmic web, but the instrument is very flexible, and scientists have used it, among other things, to study the nature of dark matter, to investigate black holes, and to refine our understanding of star formation,” says co-author Mateusz (Matt) Matuszewski (MS ’02, PhD ’12), a senior instrument scientist at Caltech.

The question of how galaxies and stars form out of a network of wispy filaments in space—what is known as the cosmic web—has fascinated Martin since he was a graduate student. To find answers, he led the teams that built both CWI and KCWI. In 2017, Martin and his team used KCWI to acquire data on two active galaxies known as quasars, named UM 287 and CSO 38, but it was not the quasars themselves they wanted to study.

Nearby each of these two quasars is a giant nebula, larger than the Milky Way and visible thanks to the strong illumination of the quasars. By looking at light emitted by hydrogen in the nebulas—specifically an atomic emission line called hydrogen Lyman-alpha—they were able to map the velocity of the gas. From previous observations at Palomar, the team already knew there were signs of rotation in the nebulas, but the Keck Observatory data revealed much more.

“When we used Palomar’s CWI previously, we were able to see what looked like a rotating disk of gas, but we couldn’t make out any filaments,” says O’Sullivan. “Now, with the increase in sensitivity and resolution with KCWI, we have more sophisticated models and can see that these objects are being fed by gas flowing in from attached filaments, which is strong evidence that the cosmic web is connected to and fueling this disk.”

Martin and colleagues developed a mathematical model to explain the velocities they were seeing in the gas and tested it on UM287 and CSO38 as well as on a simulated galaxy.

“It took us more than a year to come up with the mathematical model to explain the radial flow of the gas,” says Martin. “Once we did, we were shocked by how well the model works.”

The findings provide the best evidence to date for the cold-flow model of galaxy formation, which basically states that cool gas can flow directly into forming galaxies, where it is converted into stars. Before this model came into popularity, researchers had proposed that galaxies pull in gas and heat it up to extremely high temperatures. From there, the gas was thought to gradually cool, providing a steady but slow supply of fuel for stars.

In 1996, research from Caltech’s Charles (Chuck) Steidel, the Lee A. DuBridge Professor of Astronomy and a co-author of the new study, threw this model into question. He and his colleagues showed that distant galaxies produce stars at a very high rate—too fast to be accounted for by the slow settling and cooling of hot gas that was a favored model for young galaxy fueling.

“Through the years, we’ve acquired more and more evidence for the cold-flow model,” says Martin. “We have nicknamed our new version of the model the ‘cold-flow inspiral,’ since we see the spiraling pattern in the gas.”

“These type of measurements are exactly the kind of science we want to do with KCWI,” says John O’Meara, Keck Observatory chief scientist. “We combine the power of Keck’s telescope size, powerful instrumentation, and an amazing astronomical site to push the boundaries of what’s possible to observe. It’s very exciting to see this result in particular, since directly observing inflows has been something of a missing link in our ability to test models of galaxy formation and evolution. I can’t wait to see what’s coming next.”

The new study, titled, “Multi-Filament Inflows Fuel Young Star Forming Galaxies,” was funded by the National Science Foundation (NSF), Keck Observatory, Caltech, and the European Research Council. The galaxy simulations were performed at NASA Advanced Supercomputing at NASA Ames Research Center. Other Caltech authors include former postdoc Erika Hamden, now at the University of Arizona; Patrick Morrissey, a visitor in space astrophysics who also works at JPL, which is managed by Caltech for NASA; and research scientist James D. (Don) Neill.

About KCWI

The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope will enable studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. Support for this project was provided by Caltech, Gordon and Betty Moore Foundation, the Heising-Simons Foundation, Mt. Cuba Astronomical Foundation, NSF, and other Friends of Keck Observatory.

About W.M.Keck Observatory

The W. M. Keck Observatory telescopes are the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes atop 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. The data presented herein were obtained at the W. M. Keck Observatory, which is 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 recognize and acknowledge the very significant cultural role that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Wednesday, July 03, 2019

Atmosphere of Mid-Size Planet Revealed by Hubble and Spitzer

This artist's illustration shows the theoretical internal structure of the exoplanet GJ 3470 b. It is unlike any planet found in the Solar System. Weighing in at 12.6 Earth masses the planet is more massive than Earth but less massive than Neptune. Unlike Neptune, which is 3 billion miles from the Sun, GJ 3470 b may have formed very close to its red dwarf star as a dry, rocky object. It then gravitationally pulled in hydrogen and helium gas from a circumstellar disk to build up a thick atmosphere. The disk dissipated many billions of years ago, and the planet stopped growing. The bottom illustration shows the disk as the system may have looked long ago. Observation by NASA's Hubble and Spitzer space telescopes have chemically analyzed the composition of GJ 3470 b's very clear and deep atmosphere, yielding clues to the planet's origin. Many planets of this mass exist in our galaxy.  Credits: Artist's Illustration: NASA, ESA, and L. Hustak (STScI); Science: NASA, ESA, and B. Benneke (University of Montreal).  Hi-res image

Two NASA space telescopes have teamed up to identify, for the first time, the detailed chemical "fingerprint" of a planet between the sizes of Earth and Neptune. No planets like this can be found in our own solar system, but they are common around other stars.

The planet, Gliese 3470 b (also known as GJ 3470 b), may be a cross between Earth and Neptune, with a large rocky core buried under a deep crushing hydrogen and helium atmosphere. Weighing in at 12.6 Earth masses, the planet is more massive than Earth, but less massive than Neptune (which is more than 17 Earth masses).

Many similar worlds have been discovered by NASA's Kepler space observatory, whose mission ended in 2018. In fact, 80% of the planets in our galaxy may fall into this mass range. However, astronomers have never been able to understand the chemical nature of such a planet until now, researchers say.

By inventorying the contents of GJ 3470 b's atmosphere, astronomers are able to uncover clues about the planet's nature and origin.

"This is a big discovery from the planet formation perspective. The planet orbits very close to the star and is far less massive than Jupiter—318 times Earth's mass—but has managed to accrete the primordial hydrogen/helium atmosphere that is largely "unpolluted" by heavier elements," said Björn Benneke of the University of Montreal, Canada. "We don't have anything like this in the solar system, and that's what makes it striking."

Astronomers enlisted the combined multi-wavelength capabilities NASA's Hubble snd Spitzer space telescopes to do a first-of-a-kind study of GJ 3470 b's atmosphere.

This was accomplished by measuring the absorption of starlight as the planet passed in front of its star (transit) and the loss of reflected light from the planet as it passed behind the star (eclipse). All totaled, the space telescopes observed 12 transits and 20 eclipses. The science of analyzing chemical fingerprints based on light is called "spectroscopy."

"For the first time we have a spectroscopic signature of such a world," said Benneke. But he is at a loss for classification: Should it be called a "super-Earth" or "sub-Neptune?" Or perhaps something else?

Fortuitously, the atmosphere of GJ 3470 b turned out to be mostly clear, with only thin hazes, enabling the scientists to probe deep into the atmosphere.

"We expected an atmosphere strongly enriched in heavier elements like oxygen and carbon which are forming abundant water vapor and methane gas, similar to what we see on Neptune", said Benneke. "Instead, we found an atmosphere that is so poor in heavy elements that its composition resembles the hydrogen/helium rich composition of the Sun."

Other exoplanets called "hot Jupiters" are thought to form far from their stars, and over time migrate much closer. But this planet seems to have formed just where it is today, says Benneke.

The most plausible explanation, according to Benneke, is that GJ 3470 b was born precariously close to its red dwarf star, which is about half the mass of our Sun. He hypothesizes that essentially it started out as a dry rock, and rapidly accreted hydrogen from a primordial disk of gas when its star was very young. The disk is called a "protoplanetary disk."

"We're seeing an object that was able to accrete hydrogen from the protoplanetary disk, but didn’t runaway to become a hot Jupiter," said Benneke. "This is an intriguing regime."

One explanation is that the disk dissipated before the planet could bulk up further. "The planet got stuck being a sub-Neptune," said Benneke.

NASA's upcoming James Webb Space Telescope will be able to probe even deeper into GJ 3470 b's atmosphere thanks to the Webb's unprecedented sensitivity in the infrared. The new results have already spawned large interest by American and Canadian teams developing the instruments on Webb. They will observe the transits and eclipses of GJ 3470 b at light wavelengths where the atmospheric hazes become increasingly transparent.

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.

The Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington, D.C. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations are based at Lockheed Martin Space Systems in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

Editor: Lynn Jenner

Tuesday, July 02, 2019

Hubble captures the galaxy's biggest ongoing stellar fireworks show

Eta Carinae (Observations in UV Light Uncover Magnesium Embedded in Warm Gas)
Credit: NASA, ESA, N. Smith (University of Arizona), and J. Morse (BoldlyGo Institute

Imagine slow-motion fireworks that started exploding 170 years ago and are still continuing. This type of firework is not launched into Earth's atmosphere, but rather into space by a doomed super-massive star, called Eta Carinae, the largest member of a double-star system. A new view from NASA's Hubble Space Telescope, which includes ultraviolet light, shows the star's hot, expanding gases glowing in red, white, and blue. Eta Carinae resides 7,500 light-years away.

The celestial outburst takes the shape of a pair of ballooning lobes of dust and gas and other filaments that were blown out from the petulant star. The star may have initially weighed more than 150 Suns. For decades, astronomers have speculated about whether it is on the brink of total destruction.

The fireworks started in the 1840s when Eta Carinae went through a titanic outburst, called the Great Eruption, making it the second-brightest star visible in the sky for over a decade. Eta Carinae, in fact, was so bright that for a time it became an important navigational star for mariners in the southern seas.

The star has faded since that eruption and is now barely visible to the unaided eye. But the fireworks aren't over yet because Eta Carinae still survives. Astronomers have used almost every instrument on Hubble over the past 25 years to study the rambunctious star.

Using Hubble's Wide Field Camera 3 to map the ultraviolet-light glow of magnesium embedded in warm gas (shown in blue), astronomers were surprised to discover the gas in places they had not seen it before.

Scientists have long known that the outer material thrown off in the 1840s eruption has been heated by shock waves after crashing into the doomed star's previously ejected material. In the new images, the team had expected to find light from magnesium coming from the same complicated array of filaments as seen in the glowing nitrogen (shown in red). Instead, a completely new luminous magnesium structure was found in the space between the dusty bipolar bubbles and the outer shock-heated nitrogen-rich filaments.

"We've discovered a large amount of warm gas that was ejected in the Great Eruption but hasn't yet collided with the other material surrounding Eta Carinae," explained Nathan Smith of Steward Observatory at the University of Arizona in Tucson, Arizona, lead investigator of the Hubble program. "Most of the emission is located where we expected to find an empty cavity. This extra material is fast, and it 'ups the ante' in terms of the total energy for an already powerful stellar blast."

The newly revealed gas is important for understanding how the eruption began, because it represents the fast and energetic ejection of material that may have been expelled by the star shortly before the expulsion of the bipolar lobes. Astronomers need more observations to measure exactly how fast the material is moving and when it was ejected.

The streaks visible in the blue region outside the lower-left lobe are a striking feature in the image. These streaks are created when the star's light rays poke through the dust clumps scattered along the bubble's surface. Wherever the ultraviolet light strikes the dense dust, it leaves a long, thin shadow that extends beyond the lobe into the surrounding gas. "The pattern of light and shadow is reminiscent of sunbeams that we see in our atmosphere when sunlight streams past the edge of a cloud, though the physical mechanism creating Eta Carinae's light is different," noted team member Jon Morse of BoldlyGo Institute in New York.

This technique of searching in ultraviolet light for warm gas could be used to study other stars and gaseous nebulas, the researchers say.

"We had used Hubble for decades to study Eta Carinae in visible and infrared light, and we thought we had a pretty full accounting of its ejected debris. But this new ultraviolet-light image looks astonishingly different, revealing gas we did not see in other visible-light or infrared images," Smith said. "We're excited by the prospect that this type of ultraviolet magnesium emission may also expose previously hidden gas in other types of objects that eject material, such as protostars or other dying stars. Only Hubble can take these kinds of pictures."

Eta Carinae has had a violent history, prone to chaotic eruptions that blast parts of itself into space like an interstellar geyser. One explanation for the monster star's antics is that the convulsions were caused by a complex interplay of as many as three stars, all gravitationally bound in one system. In this scenario, the most massive member would have swallowed one of the stars, igniting the massive Great Eruption of the mid-1800s. Evidence for that event lies in the huge, expanding bipolar lobes of hot gas surrounding the system.

A fortuitous trick of nature also allowed astronomers in a previous Hubble study to analyze the Great Eruption in detail. Some of the light from the eruption took an indirect path to Earth and is just arriving now. The wayward light was heading away from our planet when it bounced off dust clouds lingering far from the turbulent stars and was rerouted to Earth, an effect called a "light echo."

The stellar behemoth will eventually reach its fireworks show finale when it explodes as a supernova. This may have already happened, although the geyser of light from such a brilliant blast hasn't yet reached Earth.

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.


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514 /

Nathan Smith
University of Arizona, Tucson, Arizona

Jon Morse
BoldlyGo Institute, New York, New York

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