Symphony of Stars: The Science of Stellar Sound Waves

This artist’s concept shows how sound waves travel through a hypothetical star that has an orbiting planet.
Credits: Gabriel Pérez Díaz, Instituto de Astrofísica de Canarias

We can’t hear it with our ears, but the stars in the sky are performing a concert, one that never stops. The biggest stars make the lowest, deepest sounds, like tubas and double basses. Small stars have high-pitched voices, like celestial flutes. These virtuosos don’t just play one "note" at a time, either -- our own Sun has thousands of different sound waves bouncing around inside it at any given moment.

Understanding these stellar harmonies represents a revolution in astronomy. By "listening" for stellar sound waves with telescopes, scientists can figure out what stars are made of, how old they are, how big they are and how they contribute to the evolution of our Milky Way galaxy as a whole. The technique is called asteroseismology. Just as earthquakes (or Earth’s seismic waves) tell us about the inside of Earth, stellar waves -- resulting in vibrations or "star quakes" -- reveal the secret inner workings of stars.  

NASA’s Kepler space telescope, now approaching the end of its mission, has been a key player in that revolution, delivering observations of waves in tens of thousands of stars since its 2009 launch.

NASA’s Transiting Exoplanet Survey Satellite (TESS), which launched in April 2018, may observe sound waves in up to one million red giants -- the massive, evolved stars that represent what our Sun will look like in about 5 billion years. While both Kepler and TESS are most famous for hunting for planets beyond our solar system (exoplanets), they are also powerful, sensitive tools for detecting stellar vibrations. And the more we know about stars, the more we know about planets that orbit them.

Continue reading this story

Written by Elizabeth Landau

Editor: Tony Greicius

Source: NASA/Kleper and K2

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Stellar Corpse Reveals Origin of Radioactive Molecules

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Radioactive molecules in the remains of a stellar collision

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Artist’s impression of stellar collision

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The position of Nova Vul 1670 in the constellation of Vulpecula 

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Wide-field view of the sky around Nova Vul 1670

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Observations using ALMA find radioactive isotope aluminium-26 from the remnant CK Vulpeculae

Astronomers using ALMA and NOEMA have made the first definitive detection of a radioactive molecule in interstellar space. The radioactive part of the molecule is an isotope of aluminium. The observations reveal that the isotope was dispersed into space after the collision of two stars, that left behind a remnant known as CK Vulpeculae. This is the first time that a direct observation has been made of this element from a known source. Previous identifications of this isotope have come from the detection of gamma rays, but their precise origin had been unknown.

The team, led by Tomasz Kamiński (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA), used the Atacama Large Millimeter/submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) to detect a source of the radioactive isotope aluminium-26. The source, known as CK Vulpeculae, was first seen in 1670 and at the time it appeared to observers as a bright, red “new star”. Though initially visible with the naked eye, it quickly faded and now requires powerful telescopes to see the remains of this merger, a dim central star surrounded by a halo of glowing material flowing away from it.

348 years after the initial event was observed, the remains of this explosive stellar merger have led to the clear and convincing signature of a radioactive version of aluminum, known as aluminium-26. This is the first unstable radioactive molecule definitively detected outside of the Solar System. Unstable isotopes have an excess of nuclear energy and eventually decay into a stable form.

“This first observation of this isotope in a star-like object is also important in the broader context of galactic chemical evolution,” notes Kamiński. “This is the first time an active producer of the radioactive nuclide aluminum-26 has been directly identified.”

Kamiński and his team detected the unique spectral signature of molecules made up of aluminum-26 and fluorine (²⁶AlF) in the debris surrounding CK Vulpeculae, which is about 2000 light-years from Earth. As these molecules spin and tumble through space, they emit a distinctive fingerprint of millimetre-wavelength light, a process known as rotational transition. Astronomers consider this the “gold standard” for detections of molecules [1].

The observation of this particular isotope provides fresh insights into the merger process that created CK Vulpeculae. It also demonstrates that the deep, dense, inner layers of a star, where heavy elements and radioactive isotopes are forged, can be churned up and cast into space by stellar collisions.

“We are observing the guts of a star torn apart three centuries ago by a collision,” remarked Kamiński.

The astronomers also determined that the two stars that merged were of relatively low mass, one being a red giant star with a mass somewhere between 0.8 and 2.5 times that of our Sun.

Being radioactive, aluminium-26 will decay to become more stable and in this process one of the protons in the nucleus decays into a neutron. During this process, the excited nucleus emits a photon with very high energy, which we observe as a gamma ray [2].

Previously, detections of gamma ray emission have shown that around two solar masses of aluminium-26 are present across the Milky Way, but the process that created the radioactive atoms was unknown. Furthermore, owing to the way that gamma rays are detected, their precise origin was also largely unknown. With these new measurements, astronomers have definitively detected for the first time an unstable radioisotope in a molecule outside of our Solar System.

At the same time, however, the team have concluded that the production of aluminium-26 by objects similar to CK Vulpeculae is unlikely to be the major source of aluminium-26 in the Milky Way. The mass of aluminium-26 in CK Vulpeculae is roughly a quarter of the mass of Pluto, and given that these events are so rare, it is highly unlikely that they are the sole producers of the isotope in the Milky Way galaxy. This leaves the door open for further studies into these radioactive molecules.

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Notes

[1] The characteristic molecular fingerprints are usually taken from laboratory experiments. In the case of ²⁶AlF, this method is not applicable because 26-aluminium is not present on Earth. Laboratory astrophysicists from the University of Kassel/Germany therefore used the fingerprint data of stable and abundant ²⁷AlF molecules to derive accurate data for the rare ²⁶AlF molecule.

[2] Aluminium-26 contains 13 protons and 13 neutrons in its nucleus (one neutron fewer than the stable isotope, aluminium-27). When it decays aluminium-26 becomes magnesium-26, a completely different element.

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More Information

This research was presented in the paper, Astronomical detection of a radioactive molecule ²⁶AlF in a remnant of an ancient explosion, which will appear in Nature Astronomy.

The team is composed of Tomasz Kamiński (Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA), Romuald Tylenda (N. Copernicus Astronomical Center, Warsaw, Poland), Karl M. Menten (Max-Planck-Institut für Radioastronomie, Bonn, Germany), Amanda Karakas (Monash Centre for Astrophysics, Melbourne, Australia), Jan Martin Winters (IRAM, Grenoble, France), Alexander A. Breier (Laborastrophysik, Universität Kassel, Germany), Ka Tat Wong (Monash Centre for Astrophysics, Melbourne, Australia), Thomas F. Giesen (Laborastrophysik, Universität Kassel, Germany) and Nimesh A. Patel (Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

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Links

• Research paper
• Photos of ALMA
• Blog post explaining more details

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Contacts 

Tomasz Kamiński
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts, USA
Email: tomasz.kaminski@cfa.harvard.edu

Calum Turner
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Email: pio@eso.org

Source: ESO/News

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New family photos of Mars and Saturn from Hubble

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Mars and Saturn close to opposition

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Saturn and its rings in 2018

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Stormy Mars in opposition in 2018

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The moons of Saturn

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The moons of Saturn (annotated)

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Mars in opposition in 2018 (annotated)

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Mars 2016/2018 side-by-side

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Videos

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Hubblecast 112 Light: Mars and Saturn

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Zoom on rotating Saturn

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Saturn and its orbiting moons

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The surface and the moons of Mars

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Animation of difference in Mars orientation, 2016 and 2018

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In summer 2018 the planets Mars and Saturn are, one after the other, in opposition to Earth. During this event the planets are relatively close to Earth, allowing astronomers to observe them in greater detail. Hubble took advantage of this preferred configuration and imaged both planets to continue its long-standing observation of the outer planets in the Solar System.

Since the NASA/ESA Hubble Space Telescope was launched, its goal has always been to study not only distant astronomical objects, but also the planets within our Solar System. Hubble’s high-resolution images of our planetary neighbours can only be surpassed by pictures taken from spacecraft that actually visit these bodies. However, Hubble has one advantage over space probes: it can look at these objects periodically and observe them over much longer periods than any passing probe could.

In the last months the planets Mars and Saturn have each been in opposition to Earth — Saturn on 27 June and Mars on 27 July. An opposition occurs when the Sun, Earth and an outer planet are lined up, with Earth sitting in between the Sun and the outer planet. During an opposition, a planet is fully lit by the Sun as seen from Earth, and it also marks the time when the planet is closest to Earth, allowing astronomers to see features on the planet’s surface in greater detail [1].

A month before Saturn’s opposition — on 6 June — Hubble was used to observe the ringed planet [2]. At this time Saturn was approximately 1.4 billion kilometres from Earth. The taken images show Saturn’s magnificent ring system near its maximum tilt toward Earth, allowing a spectacular view of the rings and the gaps between them. Though all of the gas giants boast rings, Saturn’s are the largest and most spectacular, stretching out to eight times the radius of the planet.

Alongside a beautiful view of the ring system, Hubble’s new image reveals a hexagonal pattern around the north pole — a stable and persistent wind feature discovered during the flyby of the Voyager 1 space probe in 1981. To the south of this feature a string of bright clouds is visible: remnants of a disintegrating storm.

While observing the planet Hubble also managed to capture images of six of Saturn’s 62 currently known moons: Dione, Enceladus, Tethys, Janus, Epimetheus, and Mimas. Scientists hypothesise that a small, wayward moon like one of these disintegrated 200 million years ago to form Saturn’s ring system.

Hubble shot the second portrait, of the planet Mars, on 18 July, just 13 days before Mars reached its closest approach to Earth. This year Mars will get as close as 57.6 million kilometres from Earth. This makes it the closest approach since 2003, when the red planet made its way closer to us than at any other time in almost 60 000 years (opo0322).

While previous images showed detailed surface features of the planet, this new image is dominated by a gigantic sandstorm enshrouding the entire planet. Still visible are the white polar caps, Terra Meridiani, the Schiaparelli Crater, and Hellas Basin — but all of these features are slightly blurred by the dust in the atmosphere.

Comparing these new images of Mars and Saturn with older data gathered by Hubble, other telescopes and even space probes allows astronomers to study how cloud patterns and large-scale structures on other planets in our Solar System change over time.

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Notes

[1] The dates of opposition and closest approach differ slightly. This difference is caused by the elliptical orbit of the planets and the fact that the orbits are not in exactly the same plane.

[2] The observations of Saturn were made as part of the Outer Planet Atmospheres Legacy (OPAL) project. OPAL is helping astronomers understand the atmospheric dynamics and evolution of the gas giant planets in our Solar System. Jupiter, Uranus and Neptune have already been observed several times as part of this project, but this is the first time Saturn was observed as part of OPAL.

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More Information

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

Image credit: NASA, ESA, STScI, M. Mutchler (STScI), A. Simon (GSFC) and the OPAL Team, J. DePasquale (STScI)

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Links

• Images of Hubble
• Images of Mars from Hubble
• Images of Saturn from Hubble
• Hubblesite release

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Contacts

Mathias Jäger

ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org

Source: ESA/Hubble/News 

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Enduring ‘Radio Rebound’ Powered by Jets from Gamma-Ray Burst

Artist impression of the "reverse shock" echoing back though the jets of the gamma-ray burst (GRB 161219B)

Credit: NRAO/AUI/NSF, S. Dagnello

ALMA's time-lapse movie showing the "afterglow" of a powerful gamma-ray burst. These images of the millimeter-wavelength light reveal details about the energy in the GRB's jets. Credit: ALMA (ESO/NAOJ/NRAO), T. Laskar; NRAO/AUI/NSF, S. Dagnello

Artist animation of a star exploding into a supernova and fueling a gamma-ray burst. Astronomers caught the enduring "afterglow" of one of these cataclysmic explosions with both ALMA and the VLA for the first time. The rebound, or reverse shock, triggered by the GRB’s powerful jets slamming into surrounding debris, lasted thousands of times longer than expected, giving astronomers an unprecedented glimpse into the structure and dynamics of the jets. Credit: NRAO/AUI/NSF; S. Dagnell.   ALMA Observatory on Vimeo

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ALMA Creates Its First-ever Movie of Cosmic Explosion

In the blink of an eye, a massive star more than 2 billion light-years away lost a million-year-long fight against gravity and collapsed, triggering a supernova and forming a black hole at its center.

This newborn black hole belched a fleeting yet astonishingly intense flash of gamma rays known as a gamma-ray burst (GRB) toward Earth, where it was detected by NASA’s Neil Gehrels Swift Observatory on 19 December 2016.

While the gamma rays from the burst disappeared from view a scant seven seconds later, longer wavelengths of light from the explosion — including X-ray, visible light, and radio — continued to shine for weeks. This allowed astronomers to study the aftermath of this fantastically energetic event, known as GRB 161219B, with many ground-based observatories, including the National Science Foundation’s Very Large Array.

The unique capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA), however, enabled a team of astronomers to make an extended study of this explosion at millimeter wavelengths, gaining new insights into this particular GRB and the size and composition of its powerful jets.

“Since ALMA sees in millimeter-wavelength light, which carries information on how the jets interact with the surrounding dust and gas, it is a powerful probe of these violent cosmic explosions,” said Tanmoy Laskar, an astronomer at the University of California, Berkeley, and a Jansky Postdoctoral Fellow of the National Radio Astronomy Observatory. Laskar is lead author of the study, which appears in the Astrophysical Journal.

These observations enabled the astronomers to produce ALMA’s first-ever time-lapse movie of a cosmic explosion, which revealed a surprisingly long-lasting reverse shockwave from the explosion echoing back through the jets. “With our current understanding of GRBs, we would normally expect a reverse shock to last only a few seconds. This one lasted a good portion of an entire day,” Laskar said.

A reverse shock occurs when material blasted away from a GRB by its jets runs into the surrounding gas. This encounter slows down the escaping material, sending a shockwave back down the jet.

Since jets are expected to last no more than a few seconds, a reverse shock should be an equally short-lived event. But that now appears not to be the case.

“For decades, astronomers thought this reverse shock would produce a bright flash of visible light, which has so far been really hard to find despite careful searches. Our ALMA observations show that we may have been looking in the wrong place, and that millimeter observations are our best hope of catching these cosmic fireworks,” said Carole Mundell of the University of Bath, and co-author of the study.

Instead, the light from the reverse shock shines most brightly at the millimeter wavelengths on timescales of about a day, which is most likely why it has been so difficult to detect previously. While the early millimeter light was created by the reverse shock, the X-ray and visible light came from the blast-wave shock riding ahead of the jet.

“What was unique about this event,” Laskar adds, “is that as the reverse shock entered the jet, it slowly but continuously transferred the jet’s energy into the forward-moving blast wave, causing the X-ray and visible light to fade much slower than expected. Astronomers have always puzzled where this extra energy in the blast wave comes from. Thanks to ALMA, we know this energy – up to 85 percent of the total in the case of GRB 161219B – is hidden in slow-moving material within the jet itself.” The bright reverse shock emission faded away within a week. The blast wave then shone through in the millimeter band, giving ALMA a chance to study the geometry of the jet.

The visible light from the blast wave at this critical time, when the outflow has slowed just enough for all of the jet to become visible at Earth, was overshadowed by the emerging supernova from the exploded star. But ALMA’s observations, unencumbered by supernova light, enabled the astronomers to constrain the opening angle of the outflow from the jet to about 13 degrees.

Understanding the shape and duration of the outflow from the star is essential for determining the true energy of the burst. In this case, the astronomers find the jets contained as much energy as our Sun puts out in a billion years.

“This is a fantastical amount of energy, but it is actually one of the least energetic events we have ever seen. Why this is so remains a mystery,” says Kate Alexander, a graduate student at Harvard University who led the VLA observations reported in this study. “Though more than two billion light-years away, this GRB is actually the nearest such event for which we have measured the detailed properties of the outflow, thanks to the combined power of ALMA and the VLA.”

The VLA, which observes at longer wavelengths, continued observing the radio emission from the reverse shock after it faded from ALMA’s view.

This is only the fourth gamma-ray burst with a convincing, multi-frequency detection of a reverse shock, the researchers note. The material around the collapsing star was about 3,000 times less dense than the average density of gas in our galaxy, and these new ALMA observations suggest that such low-density environments are essential for producing reverse shock emission, which may explain why such signatures are so rare.

“Our rapid-response observations highlight the key role ALMA can play in following up transients, revealing the energy source that powers them, and using them to map the physics of the Universe to the dawn of the first stars,” concludes Laskar. “In particular, our study demonstrates that ALMA’s superb sensitivity and new rapid-response capabilities makes it the only facility that can routinely detect reverse shocks, allowing us to probe the nature of the relativistic jets in these energetic transients, and the engines that launch and feed them.”

Source: National Radio Astronomy Observatory (NRAO)

# # #

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

Contact:

Charles Blue, 
Public Information Officer
(434) 296-0314;
cblue@nrao.edu

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This research is presented in a paper titled “First ALMA Light Curve Constrains Refreshed Reverse Shocks & Jets Magnetization in GRB 161219B,” by T. Laskar et al. in the Astrophysical Journal. [apj.aas.org]

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 National Science Council of Taiwan (NSC) 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

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First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole

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Artist’s impression of S2 passing supermassive black hole at centre of Milky Way

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Artist’s impression of S2 passing supermassive black hole at centre of Milky Way - annotated

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Orbit diagram of S2 around black hole at centre of the Milky Way

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Orbits of stars around black hole at the heart of the Milky Way

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The daily motion of the S2 star as seen with GRAVITY

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GRAVITY tracks star passing supermassive black hole

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NACO observation of the stars at the centre of the Milky Way

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Videos

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ESOcast 173: First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole

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Artist's impression of star passing close to supermassive black hole

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Zooming in on the heart of the Milky Way

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The star S2 makes a close approach to the black hole at the centre of the Milky Way

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Stars orbiting the black hole at the heart of the Milky Way

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Simulation of the orbits of stars around the black hole at the centre of the Milky Way

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Animation of the orbit of the star S2 around the galactic centre black hole

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Fulldome view of stars orbiting the black hole at the heart of the Milky Way

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Orbiting a black hole near the event horizon (fulldome)

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Close-up of a black hole near the event horizon (fulldome)

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Orbiting a black hole near the event horizon 2 (fulldome)

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Orbiting a black hole near the event horizon 3 (fulldome)

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Orbiting a black hole near the event horizon 4 (fulldome)

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Flight from the Earth to the Milky Way Black Hole

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Testing general relativity at the Galactic Centre — compilation

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Observations made with ESO’s Very Large Telescope have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile.

Obscured by thick clouds of absorbing dust, the closest supermassive black hole to the Earth lies 26 000 light-years away at the centre of the Milky Way. This gravitational monster, which has a mass four million times that of the Sun, is surrounded by a small group of stars orbiting around it at high speed. This extreme environment — the strongest gravitational field in our galaxy — makes it the perfect place to explore gravitational physics, and particularly to test Einstein’s general theory of relativity.

New infrared observations from the exquisitely sensitive GRAVITY [1], SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light [2].

The team compared the position and velocity measurements from GRAVITY and SINFONI respectively, along with previous observations of S2 using other instruments, with the predictions of Newtonian gravity, general relativity and other theories of gravity. The new results are inconsistent with Newtonian predictions and in excellent agreement with the predictions of general relativity.

These extremely precise measurements were made by an international team led by Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, in conjunction with collaborators around the world, at the Paris Observatory–PSL, the Université Grenoble Alpes, CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the Portuguese CENTRA – Centro de Astrofisica e Gravitação and ESO. The observations are the culmination of a 26-year series of ever-more-precise observations of the centre of the Milky Way using ESO instruments [3].

“This is the second time that we have observed the close passage of S2 around the black hole in our galactic centre. But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution,” explains Genzel. “We have been preparing intensely for this event over several years, as we wanted to make the most of this unique opportunity to observe general relativistic effects.”

The new measurements clearly reveal an effect called gravitational redshift. Light from the star is stretched to longer wavelengths by the very strong gravitational field of the black hole. And the change in the wavelength of light from S2 agrees precisely with that predicted by Einstein’s theory of general relativity. This is the first time that this deviation from the predictions of the simpler Newtonian theory of gravity has been observed in the motion of a star around a supermassive black hole.

The team used SINFONI to measure the velocity of S2 towards and away from Earth and the GRAVITY instrument in the VLT Interferometer (VLTI) to make extraordinarily precise measurements of the changing position of S2 in order to define the shape of its orbit. GRAVITY creates such sharp images that it can reveal the motion of the star from night to night as it passes close to the black hole — 26 000 light-years from Earth.

“Our first observations of S2 with GRAVITY, about two years ago, already showed that we would have the ideal black hole laboratory,” adds Frank Eisenhauer (MPE), Principal Investigator of GRAVITY and the SINFONI spectrograph. “During the close passage, we could even detect the faint glow around the black hole on most of the images, which allowed us to precisely follow the star on its orbit, ultimately leading to the detection of the gravitational redshift in the spectrum of S2.”

More than one hundred years after he published his paper setting out the equations of general relativity, Einstein has been proved right once more — in a much more extreme laboratory than he could have possibly imagined!

Françoise Delplancke, head of the System Engineering Department at ESO, explains the significance of the observations: “Here in the Solar System we can only test the laws of physics now and under certain circumstances. So it’s very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger.”

Continuing observations are expected to reveal another relativistic effect very soon — a small rotation of the star’s orbit, known as Schwarzschild precession — as S2 moves away from the black hole.

Xavier Barcons, ESO’s Director General, concludes: “ESO has worked with Reinhard Genzel and his team and collaborators in the ESO Member States for over a quarter of a century. It was a huge challenge to develop the uniquely powerful instruments needed to make these very delicate measurements and to deploy them at the VLT in Paranal. The discovery announced today is the very exciting result of a remarkable partnership.”

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Notes

[1] GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL / CNRS / Sorbonne Université / Univ. Paris Diderot and IPAG of Université Grenoble Alpes / CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofisica e Gravitação (Portugal) and ESO.

[2] S2 orbits the black hole every 16 years in a highly eccentric orbit that brings it within twenty billion kilometres — 120 times the distance from Earth to the Sun, or about four times the distance from the Sun to Neptune — at its closest approach to the black hole. This distance corresponds to about 1500 times the Schwarzschild radius of the black hole itself.

[3] Observations of the centre of the Milky Way must be made at longer wavelengths (in this case infrared) as the clouds of dust between the Earth and the central region strongly absorb visible light.

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More Information

This research was presented in a paper entitled “Detection of the Gravitational Redshift in the Orbit of the Star S2 near the Galactic Centre Massive Black Hole“, by the GRAVITY Collaboration, to appear in the journal Astronomy & Astrophysics on 26 July 2018.

The GRAVITY Collaboration team is composed of: R. Abuter (ESO, Garching, Germany), A. Amorim (Universidade de Lisboa, Lisbon, Portugal), N. Anugu (Universidade do Porto, Porto, Portugal), M. Bauböck (Max Planck Institute for Extraterrestrial Physics, Garching, Germany [MPE]), M. Benisty (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France [IPAG]), J.P. Berger (IPAG; ESO, Garching, Germany), N. Blind (Observatoire de Genève, Université de Genève, Versoix, Switzerland), H. Bonnet (ESO, Garching, Germany), W. Brandner (Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), A. Buron (MPE), C. Collin (LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Meudon, France [LESIA]), F. Chapron (LESIA), Y. Clénet (LESIA), V. Coudé du Foresto (LESIA), P. T. de Zeeuw (Sterrewacht Leiden, Leiden University, Leiden, The Netherlands; MPE), C. Deen (MPE), F. Delplancke-Ströbele (ESO, Garching, Germany), R. Dembet (ESO, Garching, Germany; LESIA), J. Dexter (MPE), G. Duvert (IPAG), A. Eckart (University of Cologne, Cologne, Germany; Max Planck Institute for Radio Astronomy, Bonn, Germany), F. Eisenhauer (MPE), G. Finger (ESO, Garching, Germany), N.M. Förster Schreiber (MPE), P. Fédou (LESIA), P. Garcia (Universidade do Porto, Porto, Portugal), R. Garcia Lopez (MPIA), F. Gao (MPE), E. Gendron (LESIA), R. Genzel (MPE; University of California, Berkeley, California, USA), S. Gillessen (MPE), P. Gordo (Universidade de Lisboa, Lisboa, Portugal), M. Habibi (MPE), X. Haubois (ESO, Santiago, Chile), M. Haug (ESO, Garching, Germany), F. Haußmann (MPE), Th. Henning (MPIA), S. Hippler (MPIA), M. Horrobin (University of Cologne, Cologne, Germany), Z. Hubert (LESIA; MPIA), N. Hubin (ESO, Garching, Germany), A. Jimenez Rosales (MPE), L. Jochum (ESO, Garching, Germany), L. Jocou (IPAG), A. Kaufer (ESO, Santiago, Chile), S. Kellner (Max Planck Institute for Radio Astronomy, Bonn, Germany), S. Kendrew (MPIA, ESA), P. Kervella (LESIA; MPIA), Y. Kok (MPE), M. Kulas (MPIA), S. Lacour (LESIA), V. Lapeyrère (LESIA), B. Lazareff (IPAG), J.-B. Le Bouquin (IPAG), P. Léna (LESIA), M. Lippa (MPE), R. Lenzen (MPIA), A. Mérand (ESO, Garching, Germany), E. Müller (ESO, Garching, Germany; MPIA), U. Neumann (MPIA), T. Ott (MPE), L. Palanca (ESO, Santiago, Chile), T. Paumard (LESIA), L. Pasquini (ESO, Garching, Germany), K. Perraut (IPAG), G. Perrin (LESIA), O. Pfuhl (MPE), P.M. Plewa (MPE), S. Rabien (MPE), J. Ramos (MPIA), C. Rau (MPE), G. Rodríguez-Coira (LESIA), R.-R. Rohloff (MPIA), G. Rousset (LESIA), J. Sanchez-Bermudez (ESO, Santiago, Chile; MPIA), S. Scheithauer (MPIA), M. Schöller (ESO, Garching, Germany), N. Schuler (ESO, Santiago, Chile), J. Spyromilio (ESO, Garching, Germany), O. Straub (LESIA), C. Straubmeier (University of Cologne, Cologne, Germany), E. Sturm (MPE), L.J. Tacconi (MPE), K.R.W. Tristram (ESO, Santiago, Chile), F. Vincent (LESIA), S. von Fellenberg (MPE), I. Wank (University of Cologne, Cologne, Germany), I. Waisberg (MPE), F. Widmann (MPE), E. Wieprecht (MPE), M. Wiest (University of Cologne, Cologne, Germany), E. Wiezorrek (MPE), J. Woillez (ESO, Garching, Germany), S. Yazici (MPE; University of Cologne, Cologne, Germany), D. Ziegler (LESIA) and G. Zins (ESO, Santiago, Chile).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 15 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

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Links

• Research paper in Astronomy & Astrophysics
• Preprint of paper in A&A
• Photos of the VLT
• GRAVITY webpages at the Max-Planck-Institut für extraterrestrische Physik
• MPE press release
• Successful first observations of the galactic centre with GRAVITY

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Contacts

Reinhard Genzel
Director, Max Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3280
Email: genzel@mpe.mpg.de

Frank Eisenhauer
GRAVITY Principal Investigator, Max Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 (89) 30 000 3563
Email: eisenhau@mpe.mpg.de

Stefan Gillessen
Max-Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3839
Email: ste@mpe.mpg.de

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: pio@eso.org

Hannelore Hämmerle
Public Information Officer, Max Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 (89) 30 000 3980
Email: hannelore.haemmerle@mpe.mpg.de

Source: ESO/News

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Mars Express detects liquid water hidden under planet's south pole

Radar detection of water under the south pole of Mars

Credit: ESA/NASA/JPL/ASI/Univ. Rome

Hi-res Image

Water detection under the south pole of Mars

Credit: Context map: NASA/Viking; THEMIS background: NASA/JPL-Caltech/Arizona State University; 

MARSIS data: ESA/NASA/JPL/ASI/Univ. Rome; R. Orosei et al 2018.

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Radar data collected by ESA's Mars Express point to a pond of liquid water buried under layers of ice and dust in the south polar region of Mars.

Evidence for the Red Planet's watery past is prevalent across its surface in the form of vast dried-out river valley networks and gigantic outflow channels clearly imaged by orbiting spacecraft. Orbiters, together with landers and rovers exploring the martian surface, also discovered minerals that can only form in the presence of liquid water.

But the climate has changed significantly over the course of the planet's 4.6 billion year history and liquid water cannot exist on the surface today, so scientists are looking underground. Early results from the 15-year old Mars Express spacecraft already found that water-ice exists at the planet's poles and is also buried in layers interspersed with dust.

The presence of liquid water at the base of the polar ice caps has long been suspected; after all, from studies on Earth, it is well known that the melting point of water decreases under the pressure of an overlying glacier. Moreover, the presence of salts on Mars could further reduce the melting point of water and keep the water liquid even at below-freezing temperatures.

But until now evidence from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, MARSIS, the first radar sounder ever to orbit another planet, remained inconclusive.

It has taken the persistence of scientists working with this subsurface-probing instrument to develop new techniques in order to collect as much high-resolution data as possible to confirm their exciting conclusion.

Ground-penetrating radar uses the method of sending radar pulses towards the surface and timing how long it takes for them to be reflected back to the spacecraft, and with what strength. The properties of the material that lies between influences the returned signal, which can be used to map the subsurface topography.

The radar investigation shows that south polar region of Mars is made of many layers of ice and dust down to a depth of about 1.5 km in the 200 km-wide area analysed in this study. A particularly bright radar reflection underneath the layered deposits is identified within a 20 km-wide zone.

Analysing the properties of the reflected radar signals and considering the composition of the layered deposits and expected temperature profile below the surface, the scientists interpret the bright feature as an interface between the ice and a stable body of liquid water, which could be laden with salty, saturated sediments. For MARSIS to be able to detect such a patch of water, it would need to be at least several tens of centimetres thick.

"This subsurface anomaly on Mars has radar properties matching water or water-rich sediments," says Roberto Orosei, principal investigator of the MARSIS experiment and lead author of the paper published in the journal Science today.

"This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered."

"We'd seen hints of interesting subsurface features for years but we couldn't reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low," adds Andrea Cicchetti, MARSIS operations manager and a co-author on the new paper.

"We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset: now we see things that simply were not possible before."

The finding is somewhat reminiscent of Lake Vostok, discovered some 4 km below the ice in Antarctica on Earth. Some forms of microbial life are known to thrive in Earth's subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past? Whether life has ever existed on Mars remains an open question, and is one that Mars missions, including the current European-Russian ExoMars orbiter and future rover, will continue to explore.

"The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential," says Dmitri Titov, ESA's Mars Express project scientist.

"This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbour planet and its habitability."

Mars Express launched 2 June 2003 and celebrates 15 years in orbit on 25 December this year.

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Notes for editors

"Radar evidence of subglacial liquid water on Mars" by R. Orosei et al is published in the journal Science.

The MARSIS instrument was funded by the Italian Space Agency (ASI) and NASA and developed by the University of Rome, Italy, in partnership with NASA's Jet Propulsion Laboratory.

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For more information please contact:

Roberto Orosei
MARSIS Principal Investigator
Istituto Nazionale di Astrofisica, Bologna, Italy
Email: roberto.orosei@inaf.it

Andrea Cicchetti
MARSIS Operations Manager
Istituto Nazionale di Astrofisica, Roma, Italy
Email: andrea.cicchetti@iaps.inaf.it

Dmitri Titov
ESA Mars Express Project Scientist
Email: dmitri.titov@esa.int

Markus Bauer
ESA Science Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Email: markus.bauer@esa.int

Source: ESA/Mars Express

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Radiation Maps of Jupiter's Moon Europa: Key to Future Missions

Radiation from Jupiter can destroy molecules on Europa's surface. Material from Europa's ocean that ends up on the surface will be bombarded by radiation, possibly destroying any biosignatures, or chemical signs that could imply the presence of life. Image credit: NASA/JPL-Caltech.  Large View

Map of Europa's surface showing the regions that receive the highest radiation dose (pink). Image credit: U.S. Geological Survey, NASA/JPL-Caltech, Johns Hopkins Applied Physics Laboratory, Nature Astronomy

New comprehensive mapping of the radiation pummeling Jupiter's icy moon Europa reveals where scientists should look -- and how deep they'll have to go -- when searching for signs of habitability and biosignatures. 

Since NASA's Galileo mission yielded strong evidence of a global ocean underneath Europa's icy shell in the 1990s, scientists have considered that moon one of the most promising places in our solar system to look for ingredients to support life. There's even evidence that the salty water sloshing around the moon's interior makes its way to the surface.

By studying this material from the interior, scientists developing future missions hope to learn more about the possible habitability of Europa's ocean.However, Europa's surface is bombarded by a constant and intense blast of radiation from Jupiter. This radiation can destroy or alter material transported up to the surface, making it more difficult for scientists to know if it actually represents conditions in Europa's ocean.

As scientists plan for upcoming exploration of Europa, they have grappled with many unknowns: Where is the radiation most intense? How deep do the energetic particles go? How does radiation affect what's on the surface and beneath - including potential chemical signs, or biosignatures, that could imply the presence of life.

A new scientific study, published today in Nature Astronomy, represents the most complete modeling and mapping of radiation at Europa and offers key pieces to the puzzle. The lead author is Tom Nordheim, research scientist at NASA's Jet Propulsion Laboratory, Pasadena, California. 

"If we want to understand what's going on at the surface of Europa and how that links to the ocean underneath, we need to understand the radiation," Nordheim said. "When we examine materials that have come up from the subsurface, what are we looking at? Does this tell us what is in the ocean, or is this what happened to the materials after they have been radiated?" 

Using data from Galileo's flybys of Europa two decades ago and electron measurements from NASA's Voyager 1 spacecraft, Nordheim and his team looked closely at the electrons blasting the moon's surface. They found that the radiation doses vary by location. The harshest radiation is concentrated in zones around the equator, and the radiation lessens closer to the poles. 

Mapped out, the harsh radiation zones appear as oval-shaped regions, connected at the narrow ends, that cover more than half of the moon. 

"This is the first prediction of radiation levels at each point on Europa's surface and is important information for future Europa missions," said Chris Paranicas, a co-author from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. 

Now scientists know where to find regions least altered by radiation, which could be crucial information for the JPL-led Europa Clipper, NASA's mission to orbit Jupiter and monitor Europa with about 45 close flybys. The spacecraft may launch as early as 2022 and will carry cameras, spectrometers, plasma and radar instruments to investigate the composition of the moon's surface, its ocean, and material that has been ejected from the surface. 

In his new paper, Nordheim didn't stop with a two-dimensional map. He went deeper, gauging how far below the surface the radiation penetrates, and building 3D models of the most intense radiation on Europa. The results tell us how deep scientists need to dig or drill, during a potential future Europa lander mission, to find any biosignatures that might be preserved. 

The answer varies, from 4 to 8 inches (10 to 20 centimeters) in the highest-radiation zones - down to less than 0.4 inches (1 centimeter) deep in regions of Europa at middle- and high-latitudes, toward the moon's poles.

To reach that conclusion, Nordheim tested the effect of radiation on amino acids, basic building blocks for proteins, to figure out how Europa's radiation would affect potential biosignatures. Amino acids are among the simplest molecules that qualify as a potential biosignature, the paper notes.

"The radiation that bombards Europa's surface leaves a fingerprint," said Kevin Hand, co-author of the new research and projectscientist for the potential Europa Lander mission. "If we know what that fingerprint looks like, we can better understand the nature of any organics and possible biosignatures that might be detected with future missions, be they spacecraft that fly by or land on Europa. 

Europa Clipper's mission team is examining possible orbit paths, and proposed routes pass over many regions of Europa that experience lower levels of radiation, Hand said. "That's good news for looking at potentially fresh ocean material that has not been heavily modified by the fingerprint of radiation."

JPL, a division of Caltech in Pasadena, California, manages the Europa Clipper mission for NASA's Science Mission Directorate in Washington.

For more information about NASA's Europa Clipper mission, visit:  https://www.nasa.gov/europa

News Media Contact

Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-6215
gretchen.p.mccartney@jpl.nasa.gov

Dwayne Brown / JoAnna Wendel
NASA Headquarters, Washington
202-358-1726 / 202-358-1003
dwayne.c.brown@nasa.gov / joanna.r.wendel@nasa.gov

Source: JPL-Caltech/News

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