Friday, June 22, 2018

VLT Makes Most Precise Test of Einstein’s General Relativity Outside Milky Way

Image of ESO 325-G004

Gravitational lensing of distant star-forming galaxies (schematic)

Two methods of measuring the mass of a galaxy

Galaxy cluster Abell S0740



 Video

ESOcast 166 Light: New test of Einstein’s general relativity (4K UHD)
ESOcast 166 Light: New test of Einstein’s general relativity (4K UHD)

Artist’s impression of massive object distorting spacetime
Artist’s impression of massive object distorting spacetime

Pan across ESO 325-G004
Pan across ESO 325-G004

Interview with Thomas Collett about the research
Interview with Thomas Collett about the research



Astronomers using the MUSE instrument on ESO’s Very Large Telescope in Chile, and the NASA/ESA Hubble Space Telescope, have made the most precise test yet of Einstein’s general theory of relativity outside the Milky Way. The nearby galaxy ESO 325-G004 acts as a strong gravitational lens, distorting light from a distant galaxy behind it to create an Einstein ring around its centre. By comparing the mass of ESO 325-G004 with the curvature of space around it, the astronomers found that gravity on these astronomical length-scales behaves as predicted by general relativity. This rules out some alternative theories of gravity.

Using the MUSE instrument on ESO’s VLT, a team led by Thomas Collett from the University of Portsmouth in the UK first calculated the mass of ESO 325-G004 by measuring the movement of stars within this nearby elliptical galaxy.

Collett explains “We used data from the Very Large Telescope in Chile to measure how fast the stars were moving in ESO 325-G004 — this allowed us to infer how much mass there must be in the galaxy to hold these stars in orbit.

But the team was also able to measure another aspect of gravity. Using the NASA/ESA Hubble Space Telescope, they observed an Einstein ring resulting from light from a distant galaxy being distorted by the intervening ESO 325-G004. Observing the ring allowed the astronomers to measure how light, and therefore spacetime, is being distorted by the huge mass of ESO 325-G004.

Einstein’s general theory of relativity predicts that objects deform spacetime around them, causing any light that passes by to be deflected. This results in a phenomenon known as gravitational lensing. This effect is only noticeable for very massive objects. A few hundred strong gravitational lenses are known, but most are too distant to precisely measure their mass. However, the galaxy ESO 325-G004 is one of the closest lenses, at just 450 million light-years from Earth.

Collett continues “We know the mass of the foreground galaxy from MUSE and we measured the amount of gravitational lensing we see from Hubble. We then compared these two ways to measure the strength of gravity — and the result was just what general relativity predicts, with an uncertainty of only 9 percent. This is the most precise test of general relativity outside the Milky Way to date. And this using just one galaxy!

General relativity has been tested with exquisite accuracy on Solar System scales, and the motions of stars around the black hole at the centre of the Milky Way are under detailed study, but previously there had been no precise tests on larger astronomical scales. Testing the long range properties of gravity is vital to validate our current cosmological model.

These findings may have important implications for models of gravity alternative to general relativity. These alternative theories predict that the effects of gravity on the curvature of spacetime are “scale dependent”. This means that gravity should behave differently across astronomical length-scales from the way it behaves on the smaller scales of the Solar System. Collett and his team found that this is unlikely to be true unless these differences only occur on length scales larger than 6000 light-years.

The Universe is an amazing place providing such lenses which we can use as our laboratories,” adds team member Bob Nichol, from the University of Portsmouth. “It is so satisfying to use the best telescopes in the world to challenge Einstein, only to find out how right he was.



More Information

This research was presented in a paper entitled “A precise extragalactic test of General Relativity” by Collett et al., to appear in the journal Science.

The team is composed of T. E. Collett (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK), L. J. Oldham (Institute of Astronomy, University of Cambridge, Cambridge, UK), R. Smith (Centre for Extragalactic Astronomy, Durham University, Durham, UK), M. W. Auger (Institute of Astronomy, University of Cambridge, Cambridge, UK), K. B. Westfall (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK; University of California Observatories – Lick Observatory, Santa Cruz, USA), D. Bacon (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK), R. C. Nichol (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK), K. L. Masters (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK), K. Koyama (Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK), R. van den Bosch (Max Planck Institute for Astronomy, Königstuhl, Heidelberg, Germany).

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”.



Links



Contacts

Thomas Collett
Institute of Cosmology and Gravitation — University of Portsmouth
Portsmouth, UK
Tel: +44 239 284 5146
Email: thomas.collett@port.ac.uk

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

Source: ESO/News


Thursday, June 21, 2018

'Red Nuggets' are Galactic Gold for Astronomers

Mrk 1216
Credit X-ray: NASA/CXC/MTA-Eötvös University/N. Werner et al.; 
Illustration: NASA/CXC/M.Weiss





A new study using data from NASA's Chandra X-ray Observatory indicates that black holes have squelched star formation in small, yet massive galaxies known as "red nuggets", as reported in our latest press release. The results suggest some red nugget galaxies may have used some of the untapped stellar fuel to grow their central supermassive black holes to unusually massive proportions.

Red nuggets are relics of the first massive galaxies that formed within only one billion years after the Big Bang. While most red nuggets merged with other galaxies over billions of years, a small number remained solitary. These relatively pristine red nuggets allow astronomers to study how the galaxies — and the supermassive black hole at their centers — act over billions of years of isolation.

In the latest research, astronomers used Chandra to study the hot gas in two of these isolated red nuggets, Mrk 1216, and PGC 032673. (The Chandra data, colored red, of Mrk 1216 is shown in the inset.) These two galaxies are located only 295 million and 344 million light years from Earth respectively, rather than billions of light years for the first known red nuggets, allowing for a more detailed look. The gas in the galaxy is heated to such high temperatures that it emits brightly in X-ray light, which Chandra detects. This hot gas contains the imprint of activity generated by the supermassive black holes in each of the two galaxies.

An artist's illustration (main panel) shows how material falling towards black holes can be redirected outward at high speeds due to intense gravitational and magnetic fields. These high-speed jets can tamp down the formation of stars. This happens because the blasts from the vicinity of the black hole provide a powerful source of heat, preventing the galaxy's hot interstellar gas from cooling enough to allow large numbers of stars to form.

A paper describing these results in the July 1st, 2018 issue of the Monthly Notices of the Royal Astronomical Society journal and is available online. The authors of the paper are Norbert Werner (MTA-Eötvös University Lendület Hot Universe and Astrophysics Research Group in Budapest, Hungary), Kiran Lakhchaura (MTA-Eötvös University), Rebecca Canning (Stanford University), Massimo Gaspari (Princeton University), and Aurora Simeonescu (ISAS/JAXA). 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.




Fast Facts for Mrk 1216:

Scale: About 50 arcsec across (71 million light years)
Category: Normal Galaxies & Starburst Galaxies, Black Holes
Coordinates (J2000): RA 8h 26m 19.8s | Dec -06° 46´ 23.0"
Constellation: Hydra
Observation Date: June 12, 2015
Observation Time: 3 hours 35 minutes
Obs. ID: 17061
Instrument: ACIS
References: N. Werner et al.,2018,MNRAS,477,3886. arXiv:1711.09983
Color Code: Intensity: X-ray (Red)
Distance Estimate: About 295 million light years (z=0.021328)



Tuesday, June 19, 2018

Star Shredded by Rare Breed of Black Hole

Credit X-ray: NASA/CXC/UNH/D.Lin et al, Optical: NASA/ESA/STSc




A team of researchers using data from ESA's XMM-Newton X-ray space observatory, NASA's Chandra X-ray Observatory and NASA's Swift X-Ray Telescope has found evidence for the existence of an intermediate-mass black hole (IMBH).

Scientists have strong evidence for the existence of stellar black holes, which are typically five to 30 times as massive as the Sun. They have also discovered that supermassive black holes with masses as large as billions of Suns exist in the centers of most galaxies. They have long been searching for IMBHs that would exist in between these two extremes, which would contain thousands of solar masses. Thought to be seeds that will eventually grow to become supermassive, IMBHs are especially elusive, and thus very few robust candidates have ever been found.

One of the few methods scientists can use to try to find an IMBH is to wait for a star to pass close to it and become disrupted. This event causes the black hole to emit a flare that can be observed by telescopes like Chandra. Previously, this kind of event has only been clearly seen at the center of a galaxy before, not at the outer edges.

In this new study led by Dacheng Lin of the University of New Hampshire, scientists identified a possible IMBH in observations of a large galaxy some 740 million light years away.

The image above shows the galaxy named 6dFGS gJ215022.2-055059 in data from NASA's Hubble Space Telescope (yellow), with the X-ray source inferred to contain the IMBH detected by Chandra (purple) on the outskirts. In the panel below, X-ray data from XMM-Newton over two epochs shows how the candidate IMBH brightens over time.

 XMM-Newton Images of 6dFGS gJ215022.2-055059
X-ray data from XMM-Newton over two epochs shows how the candidate IMBH brightens over time. Credit: ESA/XMM-Newton/D.Lin et al.

Given this and other observed properties, the researchers concluded that this X-ray source represents a star that was disrupted and torn apart by a black hole with a mass of around fifty thousand times that of the Sun. Such star-triggered outbursts are expected to only happen rarely from this type of black hole, so this discovery suggests that there could be many more such black holes lurking in a dormant state in galaxy peripheries across the local Universe.

In addition to telescopes mentioned above, this study, which appears online in Nature Astronomy on June 18, 2018 (and available here), used data from the Canada-France-Hawaii Telescope, the NASA/ESA Hubble Space Telescope, NAOJ's Subaru Telescope, the Southern Astrophysical Research (SOAR) Telescope, and the Gemini Observatory.

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.




Fast Facts for J2150:

Scale: About 36 arcsec across (129,000 light years)
Category: Black Holes
Coordinates (J2000): RA 21h 50m 22.5s | Dec -5° 51´ 08.2"
Constellation: Aquarius
Observation Date: September 14, 2016
Observation Time: 21 hours 25 minutes
Obs. ID: 17862
Instrument: ACIS
References: D. Lin et al., "A Luminous X-ray Outburst From an Intermediate-mass Black Hole In An Off-centre Star Cluster", Nature (sub, 14, Jun 2018). arXiv:1806.05692
Color Code: X-ray: Purple; Optical: Gold
Distance Estimate: About 740 million light years



Monday, June 18, 2018

One black hole or two? Dust clouds can explain puzzling features of active galactic nuclei

An artist’s impression of what an active galactic nucleus might look like at close quarters. The accretion disk produces the brilliant light in the centre. The broad-line region is just above the accretion disk and lost in the glare. Dust clouds are being driven upwards by the intense radiation. Credit: Peter Z. Harrington. Click  here for a full size image


Researchers at the University of California, Santa Cruz (UCSC), believe clouds of dust, rather than twin black holes, can explain the features found in active galactic nuclei (AGNs). The team publish their results today (14 June) in a paper in Monthly Notices of the Royal Astronomical Society.

Many large galaxies have an AGN, a small bright central region powered by matter spiralling into a supermassive black hole. When these black holes are vigorously swallowing matter, they are surrounded by hot, rapidly-moving gas known as the "broad-line region" (so-called because the spectral lines from this region are broadened by the rapid motion of the gas).

The emission from this gas is one of the best sources of information about the mass of the central black hole and how it is growing. The nature of this gas is however poorly understood; in particular there is less emission than expected from gas moving at certain velocities. The breakdown of simple models has led some astrophysicists to think that many AGNs might have not one but two black holes in them.

The new analysis is led by Martin Gaskell, a research associate in astronomy and astrophysics at UCSC. Rather than invoking two black holes, it explains much of the apparent complexity and variability of the emissions from the broad-line region as the results of small clouds of dust that can partially obscure the innermost regions of AGNs.

Gaskell comments: "We've shown that a lot of mysterious properties of active galactic nuclei can be explained by these small dusty clouds causing changes in what we see."

Co-author Peter Harrington, a UCSC graduate student who began work on the project as an undergraduate, explained that gas spiralling towards a galaxy's central black hole forms a flat "accretion disk", and the superheated gas in the accretion disk emits intense thermal radiation. Some of that light is "reprocessed" (absorbed and re-emitted) by hydrogen and other gases swirling above the accretion disk in the broad-line region. Above and beyond this is a region of dust.

"Once the dust crosses a certain threshold it is subjected to the strong radiation from the accretion disk", said Harrington. The authors believe this radiation is so intense that it blows the dust away from the disk, resulting in a clumpy outflow of dust clouds starting at the outer edge of the broad-line region.

The effect of the dust clouds on the light emitted is to make the light coming from behind them look fainter and redder, just as the earth's atmosphere makes the sun look fainter and redder at sunset. Gaskell and Harrington developed a computer code to model the effects of these dust clouds on observations of the broad-line region.

The two scientists also show that by including dust clouds in their model, it can replicate many features of emission from the broad-line region that have long puzzled astrophysicists. Rather than the gas having a changing, asymmetrical distribution that is hard to explain, the gas is simply in a uniform, symmetric, turbulent disk around the black hole. The apparent asymmetries and changes are due to dust clouds passing in front of the broad-line region and making the regions behind them look fainter and redder.

"We think it is a much more natural explanation of the asymmetries and changes than other more exotic theories, such as binary black holes, that have been invoked to explain them," Gaskell said. "Our explanation lets us retain the simplicity of the standard AGN model of matter spiralling onto a single black hole."




Media Contacts

Tim Stephens
University of California, Santa Cruz (UCSC)
United States
Tel: +1 (831) 459 4352
stephens@ucsc.edu
 
Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7292 3979
Mob: +44 (0)7802 877 699
rmassey@ras.ac.uk

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



Science Contact

Dr Martin Gaskell
University of California, Santa Cruz
mgaskell@ucsc.edu



Further Information

The new work appears in "Partial dust obscuration in active galactic nuclei as a cause of broad-line profile and lag variability, and apparent accretion disc inhomogeneities", C. Martin Gaskell and Peter Z. Harrington, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.



Notes for Editors

More news from the University of California Santa Cruz.

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

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

Follow the RAS on TwitterFacebook, Instagram and YouTube



Friday, June 15, 2018

Surprise discovery provides new insights into stellar deaths

Artist conception of a tidal disruption event (TDE) that happens when a star passes fatally close to a supermassive black hole, which reacts by launching a relativistic jet. Image credit: Sophia Dagnello, NRAO/AUI/NSF.  Hi-res image

Astronomers, working on a project to detect supernovas, made a surprise discovery when they found that one supernova explosion was actually a star being pulled apart by a supermassive black hole. ASTRON's Westerbork Synthesis Radio Telescope was involved in the observations.

This rare stellar death, known as a tidal disruption event, or TDE, occurs when the powerful gravity of a supermassive black hole rips apart a star that has wandered too close to the massive monster. 

Theorists have suggested that material pulled from the doomed star forms a rotating disk around the black hole, emitting intense X-rays and visible light, and launches jets of material outward from the poles of the disk close to the speed of light. 

"Never before have we been able to directly observe the formation and evolution of a jet from one of these events," said Miguel Perez-Torres, of the Astrophysical Institute of Andalucia in Granada, Spain. 

Originally, the researchers were monitoring a pair of colliding galaxies known as Arp 299, nearly 150 million light-years from Earth. This area of space is so rich in supernova explosions it has been dubbed the “supernova factory”. However, in January 2005 the researchers discovered a bright burst of infrared emission coming from the nucleus of one of these galaxies, and in July of the same year a new, distinct source of radio emission was witnessed from the same location. 

"As time passed, the new object stayed bright at infrared and radio wavelengths, but not in visible light and X-rays," said Seppo Mattila, of the University of Turku in Finland. "The most likely explanation is that thick interstellar gas and dust near the galaxy's centre absorbed the X-rays and visible light, then re-radiated it as infrared," he added. The researchers used the Nordic Optical Telescope on the Canary Islands and NASA's Spitzer space telescope to follow the object's infrared emission. 

Over the course of the next decade, the team continued to observe the radio emission using a technique known as Very Long Baseline Interferometry (VLBI). VLBI involves the remote coordination of multiple telescopes across the globe to focus on a single radio source at a given time. 

This technique provides extremely high resolution imaging when studying a radio source in space, providing the researchers with detailed data on the TDE. Telescopes in the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) were used for the observations, while the data collected was correlated at the Joint Institute for VLBI ERIC (JIVE), the Netherlands, and the Very Large Array (VLA), USA, respectively. 

This extensive monitoring revealed in 2011 that the radio-emitting portion was expanding in one direction, forming an elongation called a jet, as previously predicted by theorists. The measured expansion indicated that the material in the jet moved at an average of one-fourth the speed of light.

Most galaxies have supermassive black holes at their cores with masses that are millions to billions of times greater than the Sun. This mass is so concentrated that the resulting gravitational pull does not even allow light to escape. In this instance, the black hole is actively drawing material from its surroundings and ripping apart a star that is twice the Sun’s mass. This material forms a rotating disk around the black hole, and superfast jets of particles are launched outward – a phenomenon seen in radio galaxies and quasars. 

"Much of the time, however, supermassive black holes are not actively devouring anything, so they are in a quiet state," Perez-Torres explained. "Tidal disruption events can provide us with a unique opportunity to advance our understanding of the formation and evolution of jets in the vicinities of these powerful objects," he added. 

"Because of the dust that absorbed any visible light, this particular tidal disruption event may be just the tip of the iceberg of what until now has been a hidden population," Mattila said. "By looking for these events with infrared and radio telescopes, we may be able to discover many more, and learn from them," he said. 

Such events may have been more common in the distant Universe, so studying them could help scientists to better understand the environment in which galaxies developed billions of years ago.

Mattila and Perez-Torres led a team of 36 scientists from 26 institutions around the world in the observations of Arp 299. Their findings are published in the journal Science, which can be accessed here: http://science.sciencemag.org/lookup/doi/10.1126/science.aao4669

More information: 

The European VLBI Network (EVN) is a network of radio telescopes located primarily in Europe and Asia, with additional antennas in South Africa and Puerto Rico, which performs very high angular resolution observations of cosmic radio sources. 

Collectively the EVN forms the most sensitive radio telescope array at both centimetre wavelengths and millarcsecond resolution. The data collected at each of the individual stations is collated centrally at the correlator – a data processor housed at the Joint Institute for VLBI ERIC (JIVE) in Dwingeloo, the Netherlands.
 
The following EVN antennas observed at one or more epochs: Kunming, Seshan, Urumqi (China), Effelsberg, Wettzell (Germany), Medicina, Noto (Italy), Irbene (Latvia), Torun (Poland), Badary, Svetloe, Zelenchukskaya (Russia), Robledo, Yebes (Spain), Onsala (Sweden), Westerbork (The Netherlands), Cambridge and Jodrell Bank (The United Kingdom). 

Article: Mattila, S., Pérez-Torres, M., et al. 2018. A dust enshrouded tidal disruption event with a resolved radio jet in a galaxy merger. Science. DOI: 10.1126/science.aao4669 




Thursday, June 14, 2018

A New Experiment to Understand Dark Matter

Schematic image of a pulsar, falling in the gravitational field of the Milky Way. The two arrows indicate the direction of the attractive forces, towards the standard matter - stars, gas, etc. (yellow arrow) and towards the spherical distribution of dark matter (grey arrow). The question is, whether dark matter attracts the pulsar only by gravity or, in addition to gravity, by a yet unknown „fifth force“? © Norbert Wex, with Milky Way Image by R. Hurt (SSC), JPL-Caltech, NASA and pulsar image by NASA.


Do we have to change our view on how Dark Matter interacts with standard matter?

Is dark matter a source of a yet unknown force in addition to gravity? The mysterious dark matter is little understood and trying to understand its properties is an important challenge in modern physics and astrophysics. Researchers at the Max Planck Institute for Radio Astronomy in Bonn, Germany, have proposed a new experiment that makes use of super-dense stars to learn more about the interaction of dark matter with standard matter. This experiment already provides some improvement in constraining dark matter properties, but even more progress is promised by explorations in the centre of our Milky Way that are underway. 

The findings are published in the journal Physical Review Letters (2018 June 15 issue).



Around 1600, Galileo Galilei’s experiments brought him to the conclusion that in the gravitational field of the Earth all bodies, independent of their mass and composition feel the same acceleration. Isaac Newton performed pendulum experiments with different materials in order to verify the so-called universality of free fall and reached a precision of 1:1000. More recently, the satellite experiment MICROSCOPE managed to confirm the universality of free fall in the gravitational field of the Earth with a precision of 1:100 trillion.

These kind of experiments, however, could only test the universality of free fall towards ordinary matter, like the Earth itself whose composition is dominated by iron (32%), oxygen (30%), silicon (15%) and magnesium (14%). On large scales, however, ordinary matter seems to be only a small fraction of matter and energy in the universe.

It is believed that the so-called dark matter accounts for about 80% of the matter in our Universe. Until today, dark matter has not been observed directly. Its presence is only indirectly inferred from various astronomical observations like the rotation of galaxies, the motion of galaxy clusters, and gravitational lenses. The actual nature of dark matter is one of the most prominent questions in modern science. Many physicists believe that dark matter consists of so far undiscovered sub-atomic particles.

With the unknown nature of dark matter another important question arises: is gravity the only long-range interaction between normal matter and dark matter? In other words, does matter only feel the space-time curvature caused by dark matter, or is there another force that pulls matter towards dark matter, or maybe even pushes it away and thus reduces the overall attraction between normal matter and dark matter. That would imply a violation of the universality of free fall towards dark matter. This hypothetical force is sometimes labeled as “fifth force”, besides the well-known four fundamental interactions in nature (gravitation, electromagnetic & weak interaction, strong interaction).

At present, there are various experiments setting tight limits on such a fifth force originating from dark matter. One of the most stringent experiments uses the Earth-Moon orbit and tests for an anomalous acceleration towards the Galactic center, i.e. the center of the spherical dark matter halo of our Galaxy. The high precision of this experiment comes from Lunar Laser Ranging, where the distance to the Moon is measured with centimeter precision by bouncing laser pulses of the retro reflectors installed on the Moon.

Until today, nobody has conducted such a fifth force test with an exotic object like a neutron star. “There are two reasons that binary pulsars open up a completely new way of testing for such a fifth force between normal matter and dark matter”, says Lijing Shao from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, the first author of the publication in “Physical Review Letters”. “First, a neutron star consists of matter which cannot be constructed in a laboratory, many times denser than an atomic nucleus and consisting nearly entirely of neutrons. Moreover, the enormous gravitational fields inside a neutron star, billion times stronger than that of the Sun, could in principle greatly enhance the interaction with dark matter.”

The orbit of a binary pulsar can be obtained with high precision by measuring the arrival time of the radio signals of the pulsar with radio telescopes. For some pulsars, a precision of better than 100 nanoseconds can be achieved, corresponding to a determination of the pulsar orbit with a precision better than 30 meters.

To test the universality of free fall towards dark matter, the research team identified a particularly suitable binary pulsar, named PSR J1713+0747, which is at a distance of about 3800 light years from the Earth. This is a millisecond pulsar with a rotational period of just 4.6 milliseconds and is one of the most stable rotators amongst the known pulsar population. Moreover, it is in a nearly circular 68-day orbit with a white dwarf companion.

While pulsar astronomers usually are interested in tight binary pulsars with fast orbital motion when testing general relativity, the researchers were now looking for a slowly moving millisecond pulsar in a wide orbit. The wider the orbit, the more sensitive it reacts to a violation of the universality of free fall. If the pulsar feels a different acceleration towards dark matter than the white dwarf companion, one should see a deformation of the binary orbit over time, i.e. a change in its eccentricity.

“More than 20 years of regular high precision timing with Effelsberg and other radio telescopes of the European Pulsar Timing Array and the North American NANOGrav pulsar timing projects showed with high precision that there is no change in the eccentricity of the orbit”, explains Norbert Wex, also from MPIfR. “This means that to a high degree the neutron star feels the same kind of attraction towards dark matter as towards other forms of standard matter.”

“To make these tests even better, we are busily searching for suitable pulsars near large amounts of expected dark matter”, says Michael Kramer, director at MPIfR and head of its “Fundamental Physics in Radio Astronomy” research group. “The ideal place is the Galactic centre where we use Effelsberg and other telescopes in the world to have a look as part of our Black Hole Cam project. Once we will have the Square Kilometre Array, we can make those tests super-precise”, he concludes.



BlackHoleCam is an ERC-funded Synergy project to finally image, measure and understand astrophysical black holes. Its principal investigators, Heino Falcke, Michael Kramer and Luciano Rezzolla, test fundamental predictions of Einstein’s theory of General Relativity. The BlackHoleCam team members are active partners of the global Event Horizon Telescope Consortium (EHTC).



Contact

Dr. Lijing Shao
Phone:+49 228 525-505
Email: lshao@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Norbert Wex
Phone:+49 228 525-503
Email: wex@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Prof. Dr. Michael Kramer
Director and Head of "Fundamental Physics in Radio Astronomy" Research Dept.
Phone:+49 228 525-278
Email: mkramer@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn

Dr. Norbert Junkes
Press and Public Outreach
Phone:+49 228 525-399
Email:  njunkes@mpifr-bonn.mpg.de
Max-Planck-Institut für Radioastronomie, Bonn



Original Paper

Testing the universality of free fall towards dark matter with radio pulsars

by Lijing Shao, Norbert Wex and Michael Kramer, 2018, Physical Review Letters (PRL), June 14, Vol. 120, Iss. 24 (highlighted as Editors’ Suggestion).

PRL link will become active some time during June 14th. The article is also accessible via arXiv: arxiv.org/abs/1805.08408



Links

Radioastro­nomische Fundamental­physik
Research Department "Fundamental Physics in Radio Astronomy" at MPIfR, Bonn, Germany

BlackHoleCam (BHC)
ERC project "BlackHoleCam"

SKA
Square Kilometre Array (SKA)

EPTA
European Pulsar Timing Array (EPTA)

Radio Telescope Effelsberg
Effelsberg Radio Telescope

NANOGrav
North American Nanohertz Observatory for Gravitational Waves (NANOGrav)

MICROSCOPE
MICROSCOPE (A microsatellite to challenge the universality of free fall)



Background Articles

Pulsars
Pulsars at 50: still going strong (C. Renée James), astronomy.com

Dark Matter
Dark Matter: What’s the matter? (Jeff Hecht), nature.com

Lunar Laser Ranging
Lunar Laser Ranging Experiment, Wikipedia



Wednesday, June 13, 2018

ALMA Discovers Trio of Infant Planets around Newborn Star

ALMA Discovers Trio of Infant Planets

Planets in the making 

The young star HD 163296 in the constellation of Sagittarius

Surroundings of the young star HD 163296

ALMA Discovers Trio of Infant Planets



Videos

ESOcast 164 Light: ALMA Discovers Trio of Infant Planets (4K UHD)
ESOcast 164 Light: ALMA Discovers Trio of Infant Planets (4K UHD)

Zooming in on the young star HD 163296
Zooming in on the young star HD 163296



Two independent teams of astronomers have used ALMA to uncover convincing evidence that three young planets are in orbit around the infant star HD 163296. Using a novel planet-finding technique, the astronomers identified three disturbances in the gas-filled disc around the young star: the strongest evidence yet that newly formed planets are in orbit there. These are considered the first planets to be discovered with ALMA.

The Atacama Large Millimeter/submillimeter Array (ALMA) has transformed our understanding of protoplanetary discs — the gas- and dust-filled planet factories that encircle young stars. The rings and gaps in these discs provide intriguing circumstantial evidence for the presence of protoplanets [1]. Other phenomena, however, could also account for these tantalising features.

But now, using a novel planet-hunting technique that identifies unusual patterns in the flow of gas within a planet-forming disc around a young star, two teams of astronomers have each confirmed distinct, telltale hallmarks of newly formed planets orbiting an infant star [2].

“Measuring the flow of gas within a protoplanetary disc gives us much more certainty that planets are present around a young star,” said Christophe Pinte of Monash University in Australia and Institut de Planétologie et d'Astrophysique de Grenoble (Université de Grenoble-Alpes/CNRS) in France, and lead author on one of the two papers. “This technique offers a promising new direction to understand how planetary systems form.”

To make their respective discoveries, each team analysed ALMA observations of HD 163296, a young star about 330 light-years from Earth in the constellation of Sagittarius (The Archer) [3]. This star is about twice the mass of the Sun but is just four million years old — just a thousandth of the age of the Sun.

“We looked at the localised, small-scale motion of gas in the star’s protoplanetary disc. This entirely new approach could uncover some of the youngest planets in our galaxy, all thanks to the high-resolution images from ALMA,” said Richard Teague, an astronomer at the University of Michigan and principal author on the other paper.

Rather than focusing on the dust within the disc, which was clearly imaged in earlier ALMA observations, the astronomers instead studied carbon monoxide (CO) gas spread throughout the disc. Molecules of CO emit a very distinctive millimetre-wavelength light that ALMA can observe in great detail. Subtle changes in the wavelength of this light due to the Doppler effect reveal the motions of the gas in the disc.

The team led by Teague identified two planets located approximately 12 billion and 21 billion kilometres from the star. The other team, led by Pinte, identified a planet at about 39 billion kilometres from the star [4].

The two teams used variations on the same technique, which looks for anomalies in the flow of gas — as evidenced by the shifting wavelengths of the CO emission — that indicate the gas is interacting with a massive object [5].

The technique used by Teague, which derived averaged variations in the flow of the gas as small as a few percent, revealed the impact of multiple planets on the gas motions nearer to the star. The technique used by Pinte, which more directly measured the flow of the gas, is better suited to studying the outer portion of the disc. It allowed the authors to more accurately locate the third planet, but is restricted to larger deviations of the flow, greater than about 10%.

In both cases, the researchers identified areas where the flow of the gas did not match its surroundings — a bit like eddies around a rock in a river. By carefully analysing this motion, they could clearly see the influence of planetary bodies similar in mass to Jupiter.

This new technique allows astronomers to more precisely estimate protoplanetary masses and is less likely to produce false positives. “We are now bringing ALMA front and centre into the realm of planet detection,” said coauthor Ted Bergin of the University of Michigan.
Both teams will continue refining this method and will apply it to other discs, where they hope to better understand how atmospheres are formed and which elements and molecules are delivered to a planet at its birth.



Notes

[1] Although thousands of exoplanets have been discovered in the last two decades, detecting protoplanets remains at the cutting edge of science and there have been no unambiguous detections before now. The techniques currently used for finding exoplanets in fully formed planetary systems — such as measuring the wobble of a star or the dimming of starlight due to a transiting planet — do not lend themselves to detecting protoplanets.

[2] The motion of gas around a star in the absence of planets has a very simple, predictable pattern (Keplerian rotation) that is nearly impossible to alter both coherently and locally, so that only the presence of a relatively massive object can create such disturbances.

[3] ALMA’s stunning images of HD 163296 and other similar systems have revealed intriguing patterns of concentric rings and gaps within protoplanetary discs. These gaps may be evidence that protoplanets are ploughing the dust and gas away from their orbits, incorporating some of it into their own atmospheres. A previous study of this particular star’s disc shows that the gaps in the dust and gas overlap, suggesting that at least two planets have formed there.

These initial observations, however, merely provided circumstantial evidence and could not be used to accurately estimate the masses of the planets.

[4] These correspond to 80, 140 and 260 times the distance from the Earth to the Sun.

[5] This technique is similar to the one that led to the discovery of the planet Neptune in the nineteenth century. In that case anomalies in the motion of the planet Uranus were traced to the gravitational effect of an unknown body, which was subsequently discovered visually in 1846 and found to be the eighth planet in the Solar System.



More Information

This research was presented in two papers to appear in the same edition of the Astrophysical Journal Letters. The first is entitled “Kinematic evidence for an embedded protoplanet in a circumstellar disc”, by C. Pinte et al. and the second “A Kinematic Detection of Two Unseen Jupiter Mass Embedded Protoplanets”, by R. Teague et al.

The Pinte team is composed of: C. Pinte (Monash University, Clayton, Victoria, Australia; Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), D. J. Price (Monash University, Clayton, Victoria, Australia), F. Ménard (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), G. Duchêne (University of California, Berkeley California, USA; Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France), W.R.F. Dent (Joint ALMA Observatory, Santiago, Chile), T. Hill (Joint ALMA Observatory, Santiago, Chile), I. de Gregorio-Monsalvo (Joint ALMA Observatory, Santiago, Chile), A. Hales (Joint ALMA Observatory, Santiago, Chile; National Radio Astronomy Observatory, Charlottesville, Virginia, USA) and D. Mentiplay (Monash University, Clayton, Victoria, Australia).

The Teague team is composed of: Richard D. Teague (University of Michigan, Ann Arbor, Michigan, USA), Jaehan Bae (Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC, USA), Edwin A. Bergin (University of Michigan, Ann Arbor, Michigan, USA), Tilman Birnstiel (University Observatory, Ludwig-Maximilians-Universität München, Munich, Germany) and Daniel Foreman- Mackey (Center for Computational Astrophysics, Flatiron Institute, New York, USA).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of 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. 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”.



Links



Contacts

Christophe Pinte
Monash University
Clayton, Victoria, Australia
Tel: +61 4 90 30 24 18
Email:
christophe.pinte@univ-grenoble-alpes.fr

Richard Teague
University of Michigan
Ann Arbor, Michigan, USA
Tel: +1 734 764 3440
Email:
rteague@umich.edu

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

Source: ESO/News

Friday, June 08, 2018

Juno Solves 39-Year Old Mystery of Jupiter Lightning

This artist's concept of lightning distribution in Jupiter's northern hemisphere incorporates a JunoCam image with artistic embellishments. Data from NASA's Juno mission indicates that most of the lightning activity on Jupiter is near its poles. Image credit: NASA/JPL-Caltech/SwRI/JunoCam.  › Full image and caption



Ever since NASA's Voyager 1 spacecraft flew past Jupiter in March, 1979, scientists have wondered about the origin of Jupiter's lightning. That encounter confirmed the existence of Jovian lightning, which had been theorized for centuries. But when the venerable explorer hurtled by, the data showed that the lightning-associated radio signals didn't match the details of the radio signals produced by lightning here at Earth. 

In a new paper published in Nature today, scientists from NASA's Juno mission describe the ways in which lightning on Jupiter is actually analogous to Earth's lightning. Although, in some ways, the two types of lightning are polar opposites.

"No matter what planet you're on, lightning bolts act like radio transmitters -- sending out radio waves when they flash across a sky," said Shannon Brown of NASA's Jet Propulsion Laboratory in Pasadena, California, a Juno scientist and lead author of the paper. "But until Juno, all the lightning signals recorded by spacecraft [Voyagers 1 and 2, Galileo, Cassini] were limited to either visual detections or from the kilohertz range of the radio spectrum, despite a search for signals in the megahertz range. Many theories were offered up to explain it, but no one theory could ever get traction as the answer."

Enter Juno, which has been orbiting Jupiter since July 4, 2016. Among its suite of highly sensitive instruments is the Microwave Radiometer Instrument (MWR), which records emissions from the gas giant across a wide spectrum of frequencies. 

"In the data from our first eight flybys, Juno's MWR detected 377 lightning discharges," said Brown. "They were recorded in the megahertz as well as gigahertz range, which is what you can find with terrestrial lightning emissions. We think the reason we are the only ones who can see it is because Juno is flying closer to the lighting than ever before, and we are searching at a radio frequency that passes easily through Jupiter's ionosphere." 

While the revelation showed how Jupiter lightning is similar to Earth's, the new paper also notes that where these lightning bolts flash on each planet is actually quite different.

"Jupiter lightning distribution is inside out relative to Earth," said Brown. "There is a lot of activity near Jupiter's poles but none near the equator. You can ask anybody who lives in the tropics -- this doesn't hold true for our planet."

Why do lightning bolts congregate near the equator on Earth and near the poles on Jupiter? Follow the heat. 

Earth's derives the vast majority of its heat externally from solar radiation, courtesy of our Sun. 

Because our equator bears the brunt of this sunshine, warm moist air rises (through convection) more freely there, which fuels towering thunderstorms that produce lightning. 

Jupiter's orbit is five times farther from the Sun than Earth's orbit, which means that the giant planet receives 25 times less sunlight than Earth. But even though Jupiter's atmosphere derives the majority of its heat from within the planet itself, this doesn't render the Sun's rays irrelevant. They do provide some warmth, heating up Jupiter's equator more than the poles -- just as they heat up Earth. Scientists believe that this heating at Jupiter's equator is just enough to create stability in the upper atmosphere, inhibiting the rise of warm air from within. The poles, which do not have this upper-level warmth and therefore no atmospheric stability, allow warm gases from Jupiter's interior to rise, driving convection and therefore creating the ingredients for lightning. 

"These findings could help to improve our understanding of the composition, circulation and energy flows on Jupiter," said Brown. But another question looms. "Even though we see lightning near both poles, why is it mostly recorded at Jupiter's north pole?" 

In a second Juno lightning paper published today in Nature Astronomy, Ivana Kolmašová of the Czech Academy of Sciences, Prague, and colleagues, present the largest database of lightning-generated low-frequency radio emissions around Jupiter (whistlers) to date. The data set of more than 1,600 signals, collected by Juno's Waves instrument, is almost 10 times the number recorded by Voyager 1. Juno detected peak rates of four lightning strikes per second (similar to the rates observed in thunderstorms on Earth) which is six times higher than the peak values detected by Voyager 1.

"These discoveries could only happen with Juno," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute, San Antonio. "Our unique orbit allows our spacecraft to fly closer to Jupiter than any other spacecraft in history, so the signal strength of what the planet is radiating out is a thousand times stronger. Also, our microwave and plasma wave instruments are state-of-the-art, allowing us to pick out even weak lightning signals from the cacophony of radio emissions from Jupiter. "

NASA's Juno spacecraft will make its 13th science flyby over Jupiter's mysterious cloud tops on July 16. 

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of the Southwest Research Institute in San Antonio. Juno is part of NASA's New Frontiers Program, which is managed at NASA's Marshall Space Flight Center in Huntsville, Alabama, for NASA's Science Mission Directorate. The Microwave Radiometer instrument (MWR) was built by JPL. The Juno Waves instrument was provided by the University of Iowa. Lockheed Martin Space, Denver, built the spacecraft.

More information on Juno can be found at:  https://www.nasa.gov/juno - https://www.missionjuno.swri.edu

More information about Jupiter can be found at:  https://www.nasa.gov/jupiter

The public can follow the mission on Facebook and Twitter at:  https://www.facebook.com/NASAJuno - https://www.twitter.com/NASAJuno



News Media Contact

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov

JoAnna Wendel
NASA Headquarters, Washington
202-358-1003
joanna.r.wendel@nasa.gov

Richard Lewis
University of Iowa, Iowa City
319-384-0012
richard-c-lewis@uiowa.edu

Deb Schmid
Southwest Research Institute, San Antonio
210-522-2254
dschmid@swri.org



Thursday, June 07, 2018

Chandra Scouts Nearest Star System for Possible Hazards

 Alpha Centauri
Credit X-ray: NASA/CXC/University of Colorado/T.Ayres; Optical: Zdeněk Bardon/ESO

JPEG (589.4 kb) - Large JPEG (4.7 MB) - Tiff (334.6 MB) - More Images 

Tour of Alpha Centauri - More Animations
 



A new study involving long-term monitoring of Alpha Centauri by NASA's Chandra X-ray Observatory indicates that any planets orbiting the two brightest stars are likely not being pummeled by large amounts of X-ray radiation from their host stars, as described in our press release. This is important for the viability of life in the nearest star system outside the Solar System. Chandra data from May 2nd, 2017 are seen in the pull-out, which is shown in context of a visible-light image taken from the ground of the Alpha Centauri system and its surroundings.

Alpha Centauri is a triple star system located just over four light years, or about 25 trillion miles, from Earth. While this is a large distance in terrestrial terms, it is three times closer than the next nearest Sun-like star.

The stars in the Alpha Centauri system include a pair called "A" and "B," (AB for short) which orbit relativelydow close to each other. Alpha Cen A is a near twin of our Sun in almost every way, including age, while Alpha Cen B is somewhat smaller and dimmer but still quite similar to the Sun. The third member, Alpha Cen C (also known as Proxima), is a much smaller red dwarf star that travels around the AB pair in a much larger orbit that takes it more than 10 thousand times farther from the AB pair than the Earth-Sun distance. Proxima currently holds the title of the nearest star to Earth, although AB is a very close second.

The Chandra data reveal that the prospects for life in terms of current X-ray bombardment are actually better around Alpha Cen A than for the Sun, and Alpha Cen B fares only slightly worse. Proxima, on the other hand, is a type of active red dwarf star known to frequently send out dangerous flares of X-ray radiation, and is likely hostile to life. Planets in the habitable zone around Proxima receive an average dose of X-rays about 500 times larger than the Earth, and 50,000 times larger during a big flare.

Motion of Alpha Centauri A and B
  Credit: Thomas Ayres

This movie shows Chandra observations of Alpha Centauri A and B taken about every 6 months between 2005 and 2018. Alpha Cen A is the star to the upper left. The motion of the pair from left to right is their "proper motion", showing the movement of the pair in our galaxy with respect to the solar system. The change in relative positions of the pair shows the motion in their 80 year long orbit and the wobbles show the small apparent motion (called parallax) caused by the year long orbit of the Earth around the Sun. The Chandra images are shown in black and white. To place these semi-annual images in context, the two colored circles show the expected motion of Alpha Cen A (yellow) and Alpha Cen B (orange) when taking account of proper motion, orbital motion and parallax. The size of the circles is proportional to the X-ray brightness of the source.

Tom Ayres of the University of Colorado at Boulder presented these results at the 232rd meeting of the American Astronomical Society meeting in Denver, Colorado, and some of these results were published in January 2018 in the Research Notes of the American Astronomical Society. 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



Fast Facts for Alpha Centauri:

Scale: About 2 arcmin across (2.4x10-4 light years) (2.3 billion km)
Category: Neutron Stars/X-ray Binaries
Coordinates (J2000): RA 14h 39m 37s | Dec -60° 50´ 2"
Constellation: Centaurus
Observation Date: May 2, 2017
Observation Time: 2 hours 45 minutes
Obs. ID: 16681
Instrument: HRC
References: T. Ayres, 2018, Res. Notes AAS, 2, 17
Color Code: X-ray: Blue
Distance Estimate: About 1.3 pc (4.2 light years)