Discovery of the Companions of Millisecond Pulsars

An optical image of the globular cluster, 47 Tucanae. Astronomers have identified the orbiting companions to five millisecond pulsars in this cluster and found them all to be white dwarf stars.Credit: South African Astronomical Observatory

When a star with a mass of roughly ten solar masses finishes its life, it does so in a spectacular explosion known as a supernova, leaving behind as remnant "ash" a neutron star. Neutron stars have masses of one-to-several Suns, but they are tiny in size, only tens of kilometers. Neutron stars spin rapidly, and when they have associated rotating magnetic fields to constrain charged particles, these particles emit electromagnetic radiation in a lighthouse-like beam that can sweep past the Earth with great regularity every few seconds or less. Such neutron stars are known as pulsars. Pulsars are dramatic and powerful probes of supernovae, their progenitor stars, and the properties of nuclear matter under the extreme conditions that exist in these stars.

Some pulsars called millisecond pulsars spin much more quickly, and astronomers have concluded that in order to rotate so rapidly these objects must be regularly accreting material from a nearly companion star which in a binary orbit with it; the new material helps to spin-up the neutron star, which normally would gradually slow down. There are more than 200 known millisecond pulsars. An understanding of these pulsars has been hampered, however, by the fact that only about a dozen of them have had their companion stars directly detected and studied.

CfA astronomers Maureen van den Berg, Josh Grindlay, and Peter Edmonds and their colleagues used ultraviolet images from Hubble to identify the companion stars to two millisecond pulsars located in the globular cluster 47 Tucanae. They were also able to confirm a previous but tentative identification, and to confirm two more. They report that each is of these companions is a white dwarf star – an evolved star that can no longer sustain nuclear burning and which has shrunk to a fraction of its original radius. Each of these pulsars spins more than 120 times per second, and the companions orbit quite closely with periods ranging from only 0.43 days to 1.2 days, close enough to easily satisfy the requirements needed for this kind of cosmic cannibalism as the pulsars gradually feed on material from the white dwarfs. The new work significantly increases the number of identified and characterized millisecond pulsar companions.

Reference(s):

"Discovery of Near-Ultraviolet Counterparts to Millisecond Pulsars in the Globular Cluster 47 Tucanae," L. E. Rivera-Sandoval, M. van den Berg, C. O. Heinke, H. N. Cohn, P. M. Lugger, P. Freire, J. Anderson, A. M. Serenelli, L. G. Althaus, A. M. Cool, J. E. Grindlay, P. D. Edmonds, R. Wijnands and N. Ivanova, MNRAS 453, 2707, 2015.

Source: Smithsonian Astrophysical Observatory (SAO)

If our eyes could see gravitational waves

If our eyes could see gravitational waves
Copyright: NASA/C. Henze

Hi-res JPG

Picture the scene: two gigantic black holes, each one a good fraction of the size of our Solar System spiralling around each other. Closer and closer they draw until they touch and merge into a single, even more gigantic gravitational prison.

But what would you actually see? For such a cataclysmic event, it might all take place with remarkable stealth because black holes by their very nature emit no light at all. Rather than light, it would be a different story if our eyes could see gravitational waves.

This is what the merger of two black holes would look like. It is a computer simulation of the gravitational waves that would ripple away from the titanic collision, a bit like the ripples on a pond when a pebble drops into the water.

In the case of gravitational waves, the disturbances are not in water but in the spacetime continuum. This is the mathematical ‘fabric' of space and time that Albert Einstein used to explain gravity.

Gravitational radiation has been indirectly observed but never seen directly. Its detection would open a whole new way of studying the Universe. As a result, astronomers are working on both ground-based and space-based detectors. And it is a real challenge.

Gravitational radiation is incredibly difficult to measure. The ripples cause atoms to ‘bob’ about to just 1 part in 1000 000 000 000 000 000 000. Building a detector to notice this is like measuring the distance from Earth to the Sun to the accuracy of the size of a hydrogen atom.

Following decades of technology development and experiments, detectors on the ground are nearing the required sensitivity. The first detections are expected in the next few years. But these detectors can see only half of the picture. The mass of the colliding black holes determines the frequency of the gravitational radiation.

The merger of small black holes, each about a few times the mass of the Sun, will create high-frequency gravitational waves that could be seen from the ground. But the giant black holes that sit at the heart of galaxies with masses of a million times that of the Sun will generate gravitational waves of much lower frequency. These cannot be detected with ground-based systems because seismic interference and other noise will overwhelm the signals. Hence, spaceborne observatories are needed.

ESA has selected the gravitational Universe as the focus for the third large mission in the Cosmic Vision plan, with a launch date of around 2034. 

Unlocking the gravitational Universe will require a highly ambitious mission. In preparation, ESA will launch LISA-Pathfinder this November to test some of the essential technologies needed to build confidence in future spaceborne gravitational wave observatories.

This image is from a simulation of two black holes merging and the resulting emission of gravitational radiation, published by NASA in 2012.

 Source: ESA

Pairs of Supermassive Black Holes in Galaxies May Be Rarer Than Previously Thought

At left is the galaxy J0702+5002, which the researchers concluded is not an X-shaped galaxy whose form is caused by a merger. At right is the galaxy J1043+3131, which is a "true" candidate for a merged system. Credit: Roberts, et al., NRAO/AUI/NSF

Credit: Roberts, et al.; Bill Saxton, NRAO/AUI/NSF

There may be fewer pairs of supermassive black holes orbiting each other at the cores of giant galaxies than previously thought, according to a new study by astronomers who analyzed data from the National Science Foundation's Karl G. Jansky Very Large Array (VLA) radio telescope.

Massive galaxies harbor black holes with millions of times more mass than our Sun at their centers. When two such galaxies collide, their supermassive black holes join in a close orbital dance that ultimately results in the pair combining. That process, scientists expect, is the strongest source of the long-sought, elusive gravitational waves, still yet to be directly detected.

"Gravitational waves represent the next great frontier in astrophysics, and their detection will lead to new insights on the Universe," said David Roberts of Brandeis University, lead author of the research. "It's important to have as much information as possible about the sources of these waves," he added.

Astronomers worldwide have begun programs to monitor fast-rotating pulsars throughout our Milky Way Galaxy in an attempt to detect gravitational waves. These programs seek to measure shifts in the signals from the pulsars caused by gravitational waves distorting the fabric of space-time. Pulsars are spinning, superdense neutron stars that emit lighthouse-like beams of light and radio waves that allow precise measurement of their rotation rates.

Roberts and his colleagues studied a sample of galaxies called "X-shaped radio galaxies," whose peculiar structure indicated the possibility that the radio-emitting jets of superfast particles ejected by disks of material swirling around the central black holes of these galaxies have changed directions. The change, astronomers had suggested, was caused by an earlier merger with another galaxy, causing the spin axis of the black hole as well as the jet axis to shift direction.

Working from an earlier list of 100 such objects, they collected archival data from the VLA to make new, more detailed images of 52 of them. Their analysis of the new images led them to conclude that only 11 are "genuine" candidates for galaxies that have merged, causing their radio jets to change direction. The jet changes in the other galaxies, they concluded, came from other causes.

Extrapolating from this result, the astronomers estimated that fewer than 1.3 percent of galaxies with extended radio emission have experienced mergers. This rate is five times lower than previous estimates.

"This could significantly lower the level of very-long-wave gravitational waves coming from X-shaped radio galaxies, compared to earlier estimates," Roberts said. "It will be very important to relate gravitational waves to objects we see through electromagnetic radiation, such as radio waves, in order to advance our understanding of fundamental physics," he added.

Gravitational waves, ripples in space-time, were predicted in 1916 by Albert Einstein as part of his theory of general relativity. The first evidence for such waves came from observations of a pulsar orbiting another star, a system discovered in 1974 by Joseph Taylor and Russell Hulse. Observations of this pair over several years showed that their orbits are decaying at exactly the rate predicted by Einstein's equations that indicate gravitational waves carrying energy away from the system.

Taylor and Hulse received the 1993 Nobel Prize in physics for this work, which confirmed a predicted effect of gravitational waves. However, no direct detection of such waves has yet been made.

Roberts worked with Jake Cohen and Jing Lu, Brandeis undergraduates who retrieved the data from the VLA archive and produced the images of the galaxies; and Lakshmi Saripalli and Ravi Subrahmanyan of the Raman research Institute in Bangalore, India. The researchers reported their results and analysis in a pair of papers in the Astrophysical Journal Letters and the Astrophysical Journal Supplements.

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

Contact:  

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu

Source: National Radio Astronomy Observatory (NRAO)

"Fossils" of galaxies reveal the formation and evolution of massive galaxies

"Fossils" of galaxies reveal the formation and evolution of massive galaxies

An international team led by researchers at Swiss Federal Institute of Technology in Zürich observed massive dead galaxies in the universe 4 billion years after the Big Bang with the Subaru Telescope's Multi-Object InfraRed Camera and Spectrograph (MOIRCS). They discovered that the stellar content of these galaxies is strikingly similar to that of massive elliptical galaxies seen locally. Furthermore, they identified progenitors of these dead galaxies when they were forming stars at an earlier cosmic epoch, unveiling the formation and evolution of massive galaxies across 11 billion years of cosmic time.

In the local universe, massive galaxies hosting more than about 100 billion stars are predominantly dead elliptical galaxies, that is, without any signs of star-formation activity. Many questions remain on when, how and for how long star formation occurred in such galaxies before the cessation of star formation, as well as what happened since to form the dead elliptical galaxies seen today.

In order to address these issues, the research team made use of fossil records imprinted by stars in the spectra of distant dead galaxies which give important clues to their age, metal content, and element abundances. Local massive dead galaxies are about 10 billion years old and rich in heavy elements. Also, α-elements (Note 1), which measure the duration of star formation, are more abundant than iron, indicating that these galaxies formed a large amount of stars in a very short period. The team investigated the stellar content of galaxies in the distant universe 4 billion years after the Big Bang, in order to study galaxy evolution much closer to their formation epoch.

The team took the advantage of the MOIRCS's capability to observe multiple objects simultaneously, efficiently observing a sample of 24 faint galaxies. They created a composite spectrum that would have taken 200 hours of Subaru Telescope's time for a single spectrum of comparable quality (Figure 1).

Figure 1: Composite spectrum of 24 massive dead galaxies in the universe 4 billion years after the Big Bang. The spectra is equivalent to 200 hours of Subaru Telescope's observing time. Rectangles on the spectrum indicate spectral features, which are used to calculate the ages, the amount of heavy elements and the α-element abundance in the stellar populations of these galaxies. (Credit: ETH Zürich/NAOJ)  

Analysis of the composite spectrum shows that the age of the galaxies is already 1 billion years old when observed 4 billion years after the Big Bang. They host 1.7 times more heavy elements relative to the amount of hydrogen and their α-elements are twice enhanced relative to iron than the solar values. It is the first time that the α-element abundance in stars is measured in such distant dead galaxies, and it tells us that the duration of star formation in these galaxies was shorter than 1 billion years. These results reveal that these massive dead galaxies have evolved to today without further star formation (Figure 2).

Figure 2: Cosmic evolution of the age (Left), the abundance of heavy elements (Middle) and the abundance of α-elements relative to iron (Right) of massive dead elliptical galaxies. Gray data points show the results from previous works by other studies. The colored strip in the left panel is a prediction of their evolution if such massive elliptical galaxies formed 10 to 11 billion years ago (redshift of about 2.3) and evolved without forming new stars to the present universe (redshift of zero). The prediction agrees with the observed trend very well. The middle and left panels clearly show that chemical composition of massive elliptical galaxies does not evolve over cosmic time. (Credit: ETH Zürich/NAOJ)  

What do massive dead galaxies look like when they are forming stars? To answer this, the team investigated the progenitors of their sample based on their spectral analysis. The progenitors must be star-forming galaxies in the universe 1 billion years before the observed epoch for the dead galaxies. Indeed, they do find similarly massive star-forming galaxies at the right epoch and with the right star formation rate expected from the spectra. If these active galaxies continue to create stars at the same rate, they will immediately become more massive than seen in the present universe. Therefore, these galaxies will cease star formation soon and simply age.

This study establishes a consistent picture of the history of massive galaxies over 11 billion years of cosmic time. Dr. Masato Onodera who leads the team says, "We would like to explore galaxy evolution in more detail by carrying out an object-by-object study and by extending the method to an even earlier epoch."

This research was published on 1st August 2015 in The Astrophysical Journal (Onodera et al. 2015 "The Ages, Metallicities, and Element Abundance Ratios of Massive Quenched Galaxies at z~1.6"). This work was supported by the Japan Society for the Promotion of Science (Grant ID: 23224005) and the Program for Leading Graduate Schools. The preprint of the paper is available at this link.


Member of the research team (as of the publication of Onodera et al. 2015):

• Masato Onodera, C. Marcella Carollo, Sandro Tacchella (ETH Zürich, Swizerland)
• Alvio Renzini (INAF-Padova, Italy)
• Michele Cappellari (Oxford University, UK)
• Chiara Mancini (Padova University, Italy)
• Nobuo Arimoto, Yoshihiko Yamada (Subaru Telescope, Japan)
• Emanuele Daddi (CEA/Saclay, France)
• Raphaël Gobat (KIAS, South Korea)
• Veronica Strazzullo (Ludwig Maximilians University, Germany)

Notes:

1. α-elements are elements which have an atomic number that is a multiple of 4, i.e., of the helium nucleus. In this article, it refers to elements produced by Type II supernovae such as oxygen, neon, magnesium, silicon, sulfur, calcium, and titanium. 

Source: Subaru Telescope

Too big for its boots: black hole is 30 times expected size

An image of the galaxy SAGE0536AGN, from the Vista Magellanic Clouds survey. 

The galaxy is the elliptical object in the centre of the frame.

A still frame from a movie, illustrating an active galactic nucleus, with jets of material flowing from out from a central black hole. Credit: NASA / Dana Berry / SkyWorks Digital (See http://www.nasa.gov/centers/goddard/mov/103893main_3SpeedyHotSpots.mov for the full movie). Click  here for a full size image

The central supermassive black hole of a recently discovered galaxy is far larger than should be possible, according to current theories of galactic evolution. New work, carried out by astronomers at Keele University and the University of Central Lancashire, shows that the black hole is much more massive than it should be, compared to the mass of the galaxy around it. The scientists publish their results in a paper in Monthly Notices of the Royal Astronomical Society.

The galaxy, SAGE0536AGN, was initially discovered with NASA's Spitzer space telescope in infrared light. Thought to be at least 9 billion years old, it contains an active galactic nucleus (AGN), an incredibly bright object resulting from the accretion of gas by a central supermassive black hole. The gas is accelerated to high velocities due to the black hole's immense gravitational field, causing this gas to emit light.

The team has now also confirmed the presence of the black hole by measuring the speed of the gas moving around it. Using the Southern African Large Telescope, the scientists observed that an emission line of hydrogen in the galaxy spectrum (where light is dispersed into its different colours – a similar effect is seen using a prism) is broadened through the Doppler Effect, where the wavelength (colour) of light from objects is blue- or red-shifted depending on whether they are moving towards or away from us. The degree of broadening implies that the gas is moving around at high speed, a result of the strong gravitational field of the black hole.

These data have been used to calculate the black hole's mass: the more massive the black hole, the broader the emission line. The black hole in SAGE0536AGN was found to be 350 million times the mass of the Sun.

But the mass of the galaxy itself, obtained through measurements of the movement of its stars, has been calculated to be 25 billion solar masses. This is seventy times larger than that of the black hole, but the black hole is still thirty times larger than expected for this size of galaxy.

"Galaxies have a vast mass, and so do the black holes in their cores. This one though is really too big for its boots – it simply shouldn’t be possible for it to be so large", said Dr Jacco van Loon, an astrophysicist at Keele University and the lead author on the new paper.

In ordinary galaxies the black hole would grow at the same rate as the galaxy, but in SAGE0536AGN the black hole has grown much faster, or the galaxy stopped growing prematurely. Because this galaxy was found by accident, there may be more such objects waiting to be discovered. Time will tell whether SAGE0536AGN really is an oddball, or simply the first in a new class of galaxies.

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Media contact

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x113
Mob: +44 (0)7802 877 699
rm@ras.org.uk

Science contact

Dr Jacco van Loon
Keele University
Tel: +44(0)1782 73 3331
j.t.van.loon@keele.ac.uk

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Further information

The new work appears in "An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole", Jacco Th. van Loon and Anne E. Sansom, Monthly Notices of the Royal Astronomical Society, vol. 453 (3), pp. 2341-2348, Oxford University Press.

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Notes for editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises 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 3900 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter

Source:  Royal Astronomical Society (RAS)

Radio Telescopes Could Spot Stars Hidden in the Galactic Center

In this infrared image from NASA's Spitzer Space Telescope, stellar winds flowing out from the fast-moving star Zeta Ophiuchi are creating a bow shock seen as glowing gossamer threads, which, for this star, are only seen in infrared light. A similar process in the galactic center could allow us to find stars we can't see any other way, according to new research.  High Resolution (jpg) - Low Resolution (jpg)

Cambridge, MA - The center of our Milky Way galaxy is a mysterious place. Not only is it thousands of light-years away, it's also cloaked in so much dust that most stars within are rendered invisible. Harvard researchers are proposing a new way to clear the fog and spot stars hiding there. They suggest looking for radio waves coming from supersonic stars.

"There's a lot we don’t know about the galactic center, and a lot we want to learn," says lead author Idan Ginsburg of the Harvard-Smithsonian Center for Astrophysics (CfA). "Using this technique, we think we can find stars that no one has seen before."

The long path from the center of our galaxy to Earth is so choked with dust that out of every trillion photons of visible light coming our way, only one photon will reach our telescopes. Radio waves, from a different part of the electromagnetic spectrum, have lower energies and longer wavelengths. They can pass through the dust unimpeded.

On their own, stars aren’t bright enough in the radio for us to detect them at such distances. However, if a star is traveling through gas faster than the speed of sound, the situation changes. Material blowing off of the star as a stellar wind can plow into the interstellar gases and create a shock wave. And through a process called synchrotron radiation, electrons accelerated by that shock wave produce radio emission that we could potentially detect.

"In a sense, we're looking for the cosmic equivalent of a sonic boom from an airplane," explains Ginsburg.

To create a shock wave, the star would have to be moving at a speed of thousands of miles per second. This is possible in the galactic center since the stars there are influenced by the strong gravity of a supermassive black hole. When an orbiting star reaches its closest approach to the black hole, it can easily acquire the required speed.

The researchers suggest looking for this effect from one already known star called S2. This star, which is hot and bright enough to be seen in the infrared despite all the dust, will make its closest approach to the Galactic center in late 2017 or early 2018. When it does, radio astronomers can target it to look for radio emission from its shock wave.

"S2 will be our litmus test. If it's seen in the radio, then potentially we can use this method to find smaller and fainter stars – stars that can’t be seen any other way," says co-author Avi Loeb of the CfA.

This work is reported in a paper authored by Idan Ginsburg, Xiawei Wang, Avi Loeb, and Ofer Cohen (CfA). It has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

Christine Pulliam
Media Relations Manager
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source: Harvard-Smithsonian Center for Astrophysics (CfA)

Revisiting the Veil Nebula

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Revisiting the Veil Nebula

  

 

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The Veil Nebula (ground-based view)

 

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3D image of the Veil Nebula

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Stereo image of the Veil Nebula

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Videos

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Zooming in on the Veil Nebula

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Panning across the Veil Nebula

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Moving filaments of the Veil Nebula

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The NASA/ESA Hubble Space Telescope imaged three magnificent sections of the Veil Nebula in 1997

Now, a stunning new set of images from Hubble’s Wide Field Camera 3 capture these scattered stellar remains in spectacular new detail and reveal its expansion over the last years.

Deriving its name from its delicate, draped filamentary structures, the beautiful Veil Nebula is one of the best-known supernova remnants. It formed from the violent death of a star twenty times the mass of the Sun that exploded about 8000 years ago. Located roughly 2100 light-years from Earth in the constellation of Cygnus (The Swan), this brightly coloured cloud of glowing debris spans approximately 110 light-years.

In 1997, Hubble’s Wide Field and Planetary Camera 2 (WFPC2) photographed the Veil Nebula, providing detailed views of its structure. Now, overlaying WFPC2 images with new Wide Field Camera 3 (WFC3) data provides even greater detail and allows scientists to study how far the nebula has expanded since it was photographed over 18 years ago.

Despite the nebula’s complexity and distance from us, the movement of some of its delicate structures is clearly visible — particularly the faint red hydrogen filaments. In this image, one such filament can be seen as it meanders through the middle of the brighter features that dominate the image.

Astronomers suspect that before the Veil Nebula’s source star exploded it expelled a strong stellar wind. 

This wind blew a large cavity into the surrounding interstellar gas. As the shock wave from the supernova expands outwards, it encounters the walls of this cavity — and forms the nebula’s distinctive structures. Bright filaments are produced as the shock wave interacts with a relatively dense cavity wall, whilst fainter structures are generated by regions nearly devoid of material. The Veil Nebula’s colourful appearance is generated by variations in the temperatures and densities of the chemical elements present.

The blue coloured features — outlining the cavity wall — appear smooth and curved in comparison to the fluffy green and red coloured ones. This is because the gas traced by the blue filter has more recently encountered the nebula’s shock wave, thus still maintain the original shape of the shock front. These features also contain hotter gas than the red and green coloured ones [1]. The latter excited longer ago and have subsequently diffused into more chaotic structures.

Hidden amongst these bright, chaotic structures lie a few thin, sharply edged, red coloured filaments. These faint hydrogen emission features are created through a totally different mechanism than that which generates their fluffy red companions, and they provide scientists with a snapshot of the shock front. The red colour arises after gas is swept into the shock wave — which is moving at almost 1.5 million kilometres per hour! — and the hydrogen within the gas is excited by particle collisions right at the shock front itself.

Despite utilising six full Hubble fields of view, these new WFC3 images cover just a tiny fraction of the nebula’s outer limb. Located on the west side of the supernova remnant, this section of the outer shell is in a region known as NGC 6960 or — more colloquially — the Witch’s Broom Nebula.

Notes

[1] The colours in the image have been chosen to help identifying the three different species of gas; they do not represent the real colours of the nebula.

More Information

Image credit: NASA, ESA, Hubble Heritage Team

Links

• Images of Hubble
• Link to HubbleSite release
• Uncovering the Veil nebula

Contacts

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

Source:  ESA/HUBBLE/News - Space Telescope

Hubble shears a "woolly" galaxy

 NGC 3521
Credit: ESA/Hubble & NASA and S. Smartt (Queen's University Belfast)
Acknowledgement: Robert Gendler

This new image of the spiral galaxy NGC 3521 from the NASA/ESA Hubble Space Telescope is not out of focus. Instead, the galaxy itself has a soft, woolly appearance as it a member of a class of galaxies known as flocculent spirals.

Like other flocculent galaxies, NGC 3521 lacks the clearly defined, arcing structure to its spiral arms that shows up in galaxies such as Messier 101, which are called grand design spirals. In flocculent spirals, fluffy patches of stars and dust show up here and there throughout their discs. Sometimes the tufts of stars are arranged in a generally spiralling form, as with NGC 3521, but illuminated star-filled regions can also appear as short or discontinuous spiral arms.

About 30 percent of galaxies share NGC 3521's patchiness, while approximately 10 percent have their star-forming regions wound into grand design spirals.

NGC 3521 is located almost 40 million light-years away in the constellation of Leo (The Lion). The British astronomer William Herschel discovered the object in 1784. Through backyard telescopes, NGC 3521 can have a glowing, rounded appearance, giving rise to its nickname, the Bubble Galaxy.

Source: ESA/Hubble - Space Telescope

Rosetta reveals comet's water-ice cycle

The water-ice cycle of Rosetta’s comet

Copyright Data: ESA/Rosetta/VIRTIS/INAF-IAPS/OBS DE PARIS-LESIA/DLR; M.C. De Sanctis et al (2015); 

Comet: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Comet at perihelion

Copyright ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Hapi region

Copyright: ESA/Rosetta/VIRTIS/INAF-IAPS/OBS DE PARIS-LESIA/DLR; M.C. De Sanctis et al (2015)

Water ice and surface temperature at Hapi

Copyright: ESA/Rosetta/VIRTIS/INAF-IAPS/OBS DE PARIS-LESIA/DLR; M.C. De Sanctis et al (2015)

ESA’s Rosetta spacecraft has provided evidence for a daily water-ice cycle on and near the surface of comets.

Comets are celestial bodies comprising a mixture of dust and ices, which they periodically shed as they swing towards their closest point to the Sun along their highly eccentric orbits.

As sunlight heats the frozen nucleus of a comet, the ice in it – mainly water but also other ‘volatiles’ such as carbon monoxide and carbon dioxide – turns directly into a gas.

This gas flows away from the comet, carrying dust particles along. Together, gas and dust build up the bright halo and tails that are characteristic of comets.

Rosetta arrived at Comet 67P/Churyumov–Gerasimenko in August 2014 and has been studying it up close for over a year. On 13 August 2015, the comet reached the closest point to the Sun along its 6.5-year orbit, and is now moving back towards the outer Solar System.

A key feature that Rosetta’s scientists are investigating is the way in which activity on the comet and the 

associated outgassing are driven, by monitoring the increasing activity on and around the comet since Rosetta’s arrival.

Scientists using Rosetta’s Visible, InfraRed and Thermal Imaging Spectrometer, VIRTIS, have identified a region on the comet’s surface where water ice appears and disappears in sync with its rotation period. Their findings are published today in the journal Nature.

“We found a mechanism that replenishes the surface of the comet with fresh ice at every rotation: this keeps the comet ‘alive’,” says Maria Cristina De Sanctis from INAF-IAPS in Rome, Italy, lead author of the study.

 

The team studied a set of data taken in September 2014, concentrating on a one square km region on the comet’s neck. At the time, the comet was about 500 million km from the Sun and the neck was one of the most active areas.

As the comet rotates, taking just over 12 hours to complete a full revolution, the various regions undergo different illumination.

“We saw the tell-tale signature of water ice in the spectra of the study region but only when certain portions were cast in shadow,” says Maria Cristina.

Conversely, when the Sun was shining on these regions, the ice was gone. This indicates a cyclical behaviour of water ice during each comet rotation.”

The data suggest that water ice on and a few centimetres below the surface ‘sublimates’ when illuminated by sunlight, turning it into gas that then flows away from the comet. Then, as the comet rotates and the same region falls into darkness, the surface rapidly cools again.

However, the underlying layers remain warm owing to the sunlight they received in the previous hours, and, as a result, subsurface water ice keeps sublimating and finding its way to the surface through the comet’s porous interior.

But as soon as this ‘underground’ water vapour reaches the cold surface, it freezes again, blanketing that patch of comet surface with a thin layer of fresh ice.

Eventually, as the Sun rises again over this part of the surface on the next comet day, the molecules in the newly formed ice layer are the first to sublimate and flow away from the comet, restarting the cycle.

“We suspected such a water ice cycle might be at play at comets, on the basis of theoretical models and previous observations of other comets but now, thanks to Rosetta's extensive monitoring at 67P/Churyumov–Gerasimenko, we finally have observational proof,” says Fabrizio Capaccioni, VIRTIS principal investigator at INAF-IAPS in Rome, Italy.

From these data, it is possible to estimate the relative abundance of water ice with respect to other material. 

Down to a few cm deep over the region of the portion of the comet nucleus that was surveyed, water ice accounts for 10–15% of the material and appears to be well-mixed with the other constituents.

The scientists also calculated how much water vapour was being emitted by the patch that they analysed with VIRTIS, and showed that this accounted for about 3% of the total amount of water vapour coming out from the whole comet at the same time, as measured by Rosetta’s MIRO microwave sensor.

“It is possible that many patches across the surface were undergoing the same diurnal cycle, thus providing additional contributions to the overall outgassing of the comet,” adds Dr Capaccioni.

The scientists are now busy analysing VIRTIS data collected in the following months, as the comet’s activity increased around the closest approach to the Sun.

“These initial results give us a glimpse of what is happening underneath the surface, in the comet’s interior,” concludes Matt Taylor, ESA Rosetta Project Scientist.

“Rosetta is capable of tracking changes on the comet over short as well as longer time scales, and we are looking forward to combining all of this information to understand the evolution of this and other comets.”

Notes for Editors

“The diurnal cycle of water ice on comet 67P/Churyumov-Gerasimenko,” by Maria Cristina De Sanctis et al. is published in the 24 September 2015 issue of Nature.

The results are based on images and spectra taken at visible and infrared wavelengths of light on 12–14 September 2014 with VIRTIS.

These results will be presented next week at the European Planetary Science Congress, taking place from 27 September to 2 October 2015 in Nantes, France.


About Rosetta


Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta’s Philae lander is contributed by a consortium led by DLR, MPS, CNES and ASI.


For further information, please contact:

Maria Cristina De Sanctis
INAF-IAPS, Rome, Italy
Email: mariacristina.desanctis@iaps.inaf.it

Fabrizio Capaccioni
VIRTIS principal investigator
INAF-IAPS, Rome, Italy
Email: fabrizio.capaccioni@iaps.inaf.it

Matt Taylor
ESA Rosetta Project Scientist
Email: matt.taylor@esa.int

Markus Bauer



ESA Science and Robotic Exploration Communication Officer




Tel: +31 71 565 6799





Mob: +31 61 594 3 954





Email: markus.bauer@esa.int




Source: ESA/ROSETTA

Sagittarius A*: Milky Way's Black Hole Shows Signs of Increased Chatter

Sagittarius A*

Credit NASA/CXC/MPE/G.Ponti et al; Illustration: NASA/CXC/M.Weiss

JPEG (830.9 kb)  - Large JPEG (9.2 MB) - Tiff (94.8 MB) - More Images


Tour of Sagittarius A*

 More Animations 

Three orbiting X-ray telescopes have been monitoring the supermassive black hole at the center of the Milky Way galaxy for the last decade and a half to observe its behavior, as explained in our latest press release. This long monitoring campaign has revealed some new changes in the patterns of this 4-million-solar-mass black hole known as Sagittarius A* (Sgr A*).

The bottom panel of this graphic is a view of the region around Sgr A* where red, green, and blue represent low, medium, and high-energy X-rays detected by NASA's Chandra X-ray Observatory. Sgr A* itself is not visible in this image, but is embedded in the white dot at the end of the arrow. The other two telescopes involved in the 15 years of X-ray observations were ESA's XMM-Newton and NASA's Swift Gamma Ray Burst Explorer, but their data are not included in this image.

Within the past year, the usually quiet black hole has shown an increased level of X-ray flares over its typical rate. This surge in X-ray flares coincides with the passage close to Sgr A* of a mysterious object called G2. Astronomers have been tracking G2 for years, originally thinking it was an extended cloud of gas and dust. However, after passing close to Sgr A* in late 2013 its appearance did not change much, apart from being slightly stretched by the gravity of the black hole. This led to new theories that G2 was not a gas cloud, but instead a star or pair of stars within an extended dusty cocoon.

If the G2 explanation does explain the recent rise in X-ray flares, it would be the first sign of excess material falling onto the black hole because of the cloud's close passage. Some gas would likely have been stripped off the cloud, and captured by the gravity of Sgr A*. It then could have started interacting with hot material flowing towards the black hole, resulting in an enhanced feeding rate and the production of X-ray flares. This scenario is depicted in the artist's illustrations found in the upper two panels of the graphic.

While the timing of G2's passage with the surge in X-rays from Sgr A* is intriguing, it is not yet an open-and-shut case. That is because astronomers see other black holes that appear to have behavior similar to the most recent increase of activity from Sgr A*. Therefore, it's possible this increased chatter from Sgr A* may be a common trait among supermassive black holes and unrelated to G2. Instead, it could represent, for example, a change in the strength of winds from nearby massive stars that are feeding the black hole.

The analysis included 150 Chandra and XMM-Newton observations pointed at the center of the Milky Way over the last 15 years, extending from September 1999 to November 2014. An increase in the rate and brightness of bright flares from Sgr A* occurred after mid-2014, several months after the closest approach of G2 to the huge black hole. The newest set of Chandra, XMM and Swift observations, obtained between August 30 and October 2014, revealed six bright flares within about three days, while an average of only 0.8 bright flares was expected.

A paper on these findings has been accepted by the Monthly Notices of the Royal Astronomical Society and a preprint is available online. The authors of this study were Gabriele Ponti (Max Planck Institute for Extraterrestrial Physics), Barbara De Marco (Max Planck), Mark Morris (University of California, Los Angeles), Andrea Merloni (Max Planck), Teo Muñoz-Darias (University of La Laguna, Spain), Maica Clavel (CEA Saclay, France), Darryl Haggard (Amherst College), Shuo Zhang (Columbia University), Kirpal Nandra (Max Planck), Stefan Gillassen (Max Planck), Kenji Mori (Columbia), Joseph Nielsen (Massachusetts Institute of Technology), Nanda Rea (University of Amsterdam), Natalie Degenaar (University of Cambridge), Regis Terrier (University of Paris), and Andrea Goldwurm (CEA Saclay).

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 Sagittarius A*:

Scale: Image is 5 by 5 arcmin (about 38 light years)
Category: Black Holes, Milky Way Galaxy
Coordinates (J2000): RA 17h 45m 40s | Dec -29° 00' 28.00"
Constellation: Sagittarius
Observation Date: 43 pointings from September 21, 1999 to May 18, 2009
Observation Time: 278 hours (11 days 14 hours).
Obs. ID: 242, 1561, 2943, 2951-2954, 3392, 3393, 3549, 3663, 3665, 4683, 4684, 5360, 5950-5954, 6113, 6363, 6639, 6640-6646, 7554-7759, 9169-9174, 10556
Instrument: ACIS
Also Known As: Galactic Center
References: Ponti, G et al, 2015, MNRAS (accepted); arXiv:1407.2243
Color Code: Energy: Red (2-3.3 keV), Green (3.3-4.7 keV), Blue (4.7-8 keV)
Distance Estimate: About 26,000 light years

Source: NASA’s Chandra X-ray Observatory

A Cosmic Rose With Many Names

PR Image eso1537a

The star formation region Messier 17

PR Image eso1537b

The star-forming region Messier 17 in the constellation of Sagittarius

PR Image eso1537c

Digitized Sky Survey Image of the Omega Nebula (M 17)

Videos

PR Video eso1537a

Zooming in on the star formation region Messier 17

PR Video eso1537b

A close looks at the star formation region Messier 17

This new image of the rose-coloured star forming region Messier 17 was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It is one of the sharpest images showing the entire nebula and not only reveals its full size but also retains fine detail throughout the cosmic landscape of gas clouds, dust and newborn stars.

The nebula pictured here may have had more names bestowed upon it over the ages than any other object of its kind. Although officially known as Messier 17, its nicknames include: the Omega Nebula, the Swan Nebula, the Checkmark Nebula, the Horseshoe Nebula and — lest those with more of a more marine bent miss out — the Lobster Nebula.

Messier 17 is located about 5500 light-years from Earth near the plane of the Milky Way and in the constellation of Sagittarius (The Archer). The object spans a big section of the sky — its gas and dust clouds measure about 15 light-years across. This material is fueling the birth of new stars and the wide field of view of the new picture reveals many stars in front of, in, or behind Messier 17.

The nebula appears as a complex red structure with some graduation to pink. Its colouring is a signature of glowing hydrogen gas. The short-lived blue stars that recently formed in Messier 17 emit enough ultraviolet light to heat up surrounding gas to the extent that it begins to glow brightly. In the central region the colours are lighter, and some parts appear white. This white colour is real — it arises as a result of mixing the light from the hottest gas with the starlight reflected by dust.

The gas in the nebula is estimated to have more than 30 000 times the mass of the Sun. Messier 17 also contains an open star cluster of 35 stars, which is known as NGC 6618 [1]. The total number of stars in the nebula, however, is much higher — there are almost 800 stars in the centre with even more forming in its outer regions.

Throughout this rosy glow, the nebula shows a web of darker regions of dust that obscure the light. This obscuring material is also glowing and — although these areas are dark in this visible-light image — they look bright when observed using infrared cameras.

The nebula owes its official name to the French comet hunter Charles Messier who included the nebula as the seventeenth object in his famous astronomical catalogue in 1764 [2]. But even with a name as bland as Messier 17, this flowery nebula still looks dazzling.

This picture comes from the ESO Cosmic Gems programme [3].

Notes

[1] This designation is also sometimes used for the entire star formation region.

[2] The astronomer Jean Philippe de Chéseaux discovered the object in 1745, but his discovery did not receive widespread attention. Thus, Messier independently rediscovered and catalogued it almost 20 years later.

[3] The ESO Cosmic Gems programme is an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, 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. 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, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

• 3D animation of Messier 17
• A wide view of Messier 17 from the VST
• A view of the nebula’s core from the VLT
• ESO Cosmic Gems programme

Contacts

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

Source: ESO

Watching an Exoplanet in Motion Around a Distant Star

A series of images taken between November 2013 to April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile shows the exoplanet β Pic b orbiting the star β Pictoris, which lies over 60 light-years from Earth. In the images, the star is at the centre of the left-hand edge of the frame; it is hidden by the Gemini Planet Imager’s coronagraph. We are looking at the planet’s orbit almost edge-on; the planet is closer to the Earth than the star. The images are based on observations described in a paper published in the Astrophysical Journal, 16 September 2015 and whose lead author is Maxwell Millar-Blanchaer. GPI is a groundbreaking instrument that was developed by an international team led by Stanford University’s Prof. Bruce Macintosh (a U of T alumnus) and the University of California Berkeley’s Prof. James Graham (former director of the Dunlap Institute for Astronomy & Astrophysics, U of T). Image credit: M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute. Vimeo

GIF version of animation.  

Image credit: M. Millar-Blanchaer, University of Toronto; R. Marchis (SETI Institute)

A team of astronomers has given us our best view yet of an exoplanet moving in its orbit around a distant star. A series of images captured between November 2013 to April 2015 shows the exoplanet β Pic b as it moves through 1 ½ years of its 22-year orbital period.

First discovered in 2008, β Pic b is a gas giant planet ten to twelve times the mass of Jupiter, with an orbit roughly the diameter of Saturn’s. It is part of a dynamic and complex system that includes comets, orbiting gas clouds, and an enormous debris disk that in our Solar System would extend from Neptune’s orbit to nearly two thousand times the Sun/Earth distance. Because the planet and debris disk interact gravitationally, the system provides astronomers with an ideal laboratory to test theories on the formation of planetary systems beyond ours.

Maxwell Millar-Blanchaer, a PhD-candidate in the Department of Astronomy & Astrophysics, University of Toronto, is lead author of a paper to be published September 16th in the Astrophysical Journal. The paper describes observations of the β Pictoris system made with the Gemini Planet Imager (GPI) instrument on the Gemini South telescope in Chile.

"The images in the series represent the most accurate measurements of the planet’s position ever made," says Millar-Blanchaer. "In addition, with GPI, we're able to see both the disk and the planet at the exact same time. With our combined knowledge of the disk and the planet we’re really able to get a sense of the planetary system’s architecture and how everything interacts."

The paper includes refinements to measurements of the exoplanet’s orbit and the ring of material circling the star which shed light on the dynamic relationship between the two. It also includes the most accurate measurement of the mass of β Pictoris to date and shows it is very unlikely that β Pic b will pass directly between us and its parent star.

"It’s remarkable that Gemini is not only able to directly image exoplanets but is also capable of effectively making movies of them orbiting their parent star," said Chris Davis, astronomy division program director at the National Science Foundation, which is one of five international partners that funds the Gemini twin telescopes’ operation and maintenance. "Beta Pic is a special target. The disk of gas and dust from which planets are currently forming was one of the first to be observed and is a fabulous laboratory for the study of young solar systems.”

Astronomers have discovered nearly two thousand exoplanets in the past two decades but most have been detected with instruments – like the Kepler space telescope – that use the transit method of detection: astronomers detect a faint drop in a star’s brightness as an exoplanet transits or passes between us and the star, but do not see the exoplanet itself.

With GPI, astronomers image the actual planet – a remarkable feat given that an orbiting world typically appears a million times fainter than its parent star. This is possible because GPI's adaptive optics sharpen the image of the target star by cancelling out the distortion caused by the Earth’s atmosphere; it then blocks the bright image of the star with a device called a coronagraph, revealing the exoplanet.

Laurent Pueyo is with the Space Telescope Science Institute and a co-author on the paper. "It’s fortunate that we caught β Pic b just as it was heading back – as seen from our vantage point – toward β Pictoris," says Pueyo. "This means we can make more observations before it gets too close to its parent star and that will allow us to measure its orbit even more precisely."

GPI is a groundbreaking instrument that was developed by an international team led by Stanford University’s Prof. Bruce Macintosh (a U of T alumnus) and the University of California Berkeley’s Prof. James Graham (former director of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto). In August 2015, the team announced its first exoplanet discovery: a young Jupiter-like exoplanet designated 51 Eri b. It is the first exoplanet to be discovered as part of the GPI Exoplanet Survey (GPIES) which will target 600 stars over the next three years. 

Contact:

Media Contact:

Peter Michaud 
Public Information and Outreach ManagerGemini Observatory, Hilo, HI
Email: pmichaud@gemini.edu
Cell: (808) 936-6643
Desk: (808) 974-2510

Chris Sasaki
Communications Coordinator
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
Email: media@dunlap.utoronto.ca
Phone: 416-978-6613


Science Contacts:

Max Millar-Blanchaer
Department of Astronomy and Astrophysics
University of Toronto
Email: maxmb@astro.utoronto.ca
Phone: (416) 978-3146

Fredrik Rantakyro
Gemini Observatory, La Serena, Chile
Email: frantaky@gemini.edu
Cell: 9 - 995097802
Desk: 56-51- 2205665

Joint University of Toronto and Gemini Observatory Press Release
See the Dunlop Observatory/University of Toronto version of this release here.

 Source: Gemini Observatory