Category Archives: Astronomy

ESO: The Very Large Telescope looks deeper into the Hubble Ultra Deep Field

November 29, 2017 TopSpacer 1 Comment

The latest ESO (European Southern Observatory) report:

MUSE Probes Uncharted Depths of Hubble Ultra Deep Field
Deepest ever spectroscopic survey completed

This colour image shows the Hubble Ultra Deep Field region, a tiny but much-studied region in the constellation of Fornax, as observed with the MUSE instrument on ESO’s Very Large Telescope. But this picture only gives a very partial view of the riches of the MUSE data, which also provide a spectrum for each pixel in the picture. This data set has allowed astronomers not only to measure distances for far more of these galaxies than before — a total of 1600 — but also to find out much more about each of them. Surprisingly 72 new galaxies were found that had eluded deep imaging with the NASA/ESA Hubble Space Telescope. [Hi-res images]

Astronomers using the MUSE instrument on ESO’s Very Large Telescope in Chile have conducted the deepest spectroscopic survey ever. They focused on the Hubble Ultra Deep Field, measuring distances and properties of 1600 very faint galaxies including 72 galaxies that have never been detected before, even by Hubble itself. This groundbreaking dataset has already resulted in 10 science papers that are being published in a special issue of Astronomy & Astrophysics. This wealth of new information is giving astronomers insight into star formation in the early Universe, and allows them to study the motions and other properties of early galaxies — made possible by MUSE’s unique spectroscopic capabilities.

The MUSE HUDF Survey team, led by Roland Bacon of the Centre de recherche astrophysique de Lyon (CNRS/Université Claude Bernard Lyon 1/ENS de Lyon), France, used MUSE (Multi Unit Spectroscopic Explorer) to observe the Hubble Ultra Deep Field (heic0406), a much-studied patch of the southern constellation of Fornax (The Furnace). This resulted in the deepest spectroscopic observations ever made; precise spectroscopic information was measured for 1600 galaxies, ten times as many galaxies as has been painstakingly obtained in this field over the last decade by ground-based telescopes.

This image shows the Hubble Ultra Deep Field 2012, an improved version of the Hubble Ultra Deep Field image featuring additional observation time. The new data have revealed for the first time a population of distant galaxies at redshifts between 9 and 12, including the most distant object observed to date. These galaxies will require confirmation using spectroscopy by the forthcoming NASA/ESA/CSA James Webb Space Telescope before they are considered to be fully confirmed. [Higher res images.]

The original HUDF images were pioneering deep-field observations with the NASA/ESA Hubble Space Telescope published in 2004. They probed more deeply than ever before and revealed a menagerie of galaxies dating back to less than a billion years after the Big Bang. The area was subsequently observed many times by Hubble and other telescopes, resulting in the deepest view of the Universe to date [1]. Now, despite the depth of the Hubble observations, MUSE has — among many other results — revealed 72 galaxies never seen before in this very tiny area of the sky.

Roland Bacon takes up the story:

“MUSE can do something that Hubble can’t — it splits up the light from every point in the image into its component colours to create a spectrum. This allows us to measure the distance, colours and other properties of all the galaxies we can see — including some that are invisible to Hubble itself.”

The MUSE data provides a new view of dim, very distant galaxies, seen near the beginning of the Universe about 13 billion years ago. It has detected galaxies 100 times fainter than in previous surveys, adding to an already richly observed field and deepening our understanding of galaxies across the ages.

The survey unearthed 72 candidate galaxies known as Lyman-alpha emitters that shine only in Lyman-alpha light [2]. Current understanding of star formation cannot fully explain these galaxies, which just seem to shine brightly in this one colour. Because MUSE disperses the light into its component colours these objects become apparent, but they remain invisible in deep direct images such as those from Hubble.

“MUSE has the unique ability to extract information about some of the earliest galaxies in the Universe — even in a part of the sky that is already very well studied,” explains Jarle Brinchmann, lead author of one of the papers describing results from this survey, from the University of Leiden in the Netherlands and the Institute of Astrophysics and Space Sciences at CAUP in Porto, Portugal. “We learn things about these galaxies that is only possible with spectroscopy, such as chemical content and internal motions — not galaxy by galaxy but all at once for all the galaxies!”

Another major finding of this study was the systematic detection of luminous hydrogen halos around galaxies in the early Universe, giving astronomers a new and promising way to study how material flows in and out of early galaxies.

Many other potential applications of this dataset are explored in the series of papers, and they include studying the role of faint galaxies during cosmic reionisation (starting just 380 000 years after the Big Bang), galaxy merger rates when the Universe was young, galactic winds, star formation as well as mapping the motions of stars in the early Universe.

“Remarkably, these data were all taken without the use of MUSE’s recent Adaptive Optics Facility upgrade. The activation of the AOF after a decade of intensive work by ESO’s astronomers and engineers promises yet more revolutionary data in the future,” concludes Roland Bacon [3].

Notes
>[1] The Hubble Ultra Deep Field is one of the most extensively studied areas of space. To date, 13 instruments on eight telescopes, including the ESO-partnered ALMA (eso1633), have observed the field from X-ray to radio wavelengths.

[2] The negatively-charged electrons that orbit the positively-charged nucleus in an atom have quantised energy levels. That is, they can only exist in specific energy states, and they can only transition between them by gaining or losing precise amounts of energy. Lyman-alpha radiation is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. The precise amount of energy lost is released as light with a particular wavelength in the ultraviolet part of the spectrum, which astronomers can detect with space telescopes or on Earth in the case of redshifted objects. For this data, at redshift of z ~ 3–6.6, the Lyman-alpha light is seen as visible or near-infrared light.

[3] The Adaptive Optics Facility with MUSE has already revealed previously unseen rings around the planetary nebula IC 4406 (eso1724).

Asteroids & Comets, Astronomy

ESO: VLT detects unusual features of first observed interstellar asteroid

November 20, 2017 TopSpacer 1 Comment

A new report from the ESO (European Southern Observatory):

ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before

This artist’s impression shows the first interstellar asteroid: `Oumuamua. This unique object was discovered on 19 October 2017 by the Pan-STARRS 1 telescope in Hawai`i. Subsequent observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that it was travelling through space for millions of years before its chance encounter with our star system. `Oumuamua seems to be a dark red highly-elongated metallic or rocky object, about 400 metres long, and is unlike anything normally found in the Solar System. [Larger images.]

For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.

On 19 October 2017, the Pan-STARRS 1 telescope in Hawai`i picked up a faint point of light moving across the sky. It initially looked like a typical fast-moving small asteroid, but additional observations over the next couple of days allowed its orbit to be computed fairly accurately. The orbit calculations revealed beyond any doubt that this body did not originate from inside the Solar System, like all other asteroids or comets ever observed, but instead had come from interstellar space. Although originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it passed closest to the Sun in September 2017. The object was reclassified as an interstellar asteroid and named 1I/2017 U1 (`Oumuamua) [1].

“We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”

ESO’s Very Large Telescope was immediately called into action to measure the object’s orbit, brightness and colour more accurately than smaller telescopes could achieve. Speed was vital as `Oumuamua was rapidly fading as it headed away from the Sun and past the Earth’s orbit, on its way out of the Solar System. There were more surprises to come.

This very deep combined image shows the interstellar asteroid ‘Oumuamua at the centre of the picture. It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving asteroid. This image was created by combining multiple images from ESO’s Very Large Telescope as well as the Gemini South Telescope. The object is marked with a blue circle and appears to be a point source, with no surrounding dust. [ Larger Images. ]

Combining the images from the FORS instrument on the VLT using four different filters with those of other large telescopes, the team of astronomers led by Karen Meech (Institute for Astronomy, Hawai`i, USA) found that `Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.

Karen Meech explains the significance:

“This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”

These properties suggest that `Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years. It is estimated to be at least 400 metres long.

This diagram shows the orbit of the interstellar asteroid ‘Oumuamua as it passes through the Solar System. Unlike all other asteroids and comets observed before, this body is not bound by gravity to the Sun. It has come from interstellar space and will return there after its brief encounter with our star system. Its hyperbolic orbit is highly inclined and it does not appear to have come close to any other Solar System body on its way in. [Larger images.]

Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago. `Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.

https://youtu.be/O6PpbO7vIjU

Astronomers estimate that an interstellar asteroid similar to `Oumuamua passes through the inner Solar System about once per year, but they are faint and hard to spot so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.

“We are continuing to observe this unique object,” concludes Olivier Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”

Notes
[1] The Pan-STARRS team’s proposal to name the interstellar objet was accepted by the International Astronomical Union, which is responsible for granting official names to bodies in the Solar System and beyond. The name is Hawaiian and more details are given here. The IAU also created a new class of objects for interstellar asteroids, with this object being the first to receive this designation. The correct forms for referring to this object are now: 1I, 1I/2017 U1, 1I/`Oumuamua and 1I/2017 U1 (`Oumuamua). Note that the character before the O is an okina. So, the name should sound like H O u mu a mu a. Before the introduction of the new scheme, the object was referred to as A/2017 U1.

Astronomy

ESO: Nearest temperate world found orbiting quiet star

November 15, 2017 TopSpacer 1 Comment

The latest report from ESO (European Southern Observatory):

Closest Temperate World Orbiting Quiet Star Discovered
ESO’s HARPS instrument finds Earth-mass exoplanet around Ross 128

This artist’s impression shows the temperate planet Ross 128 b, with its red dwarf parent star in the background. This planet, which lies only 11 light-years from Earth, was found by a team using ESO’s unique planet-hunting HARPS instrument. The new world is now the second-closest temperate planet to be detected after Proxima b. It is also the closest planet to be discovered orbiting an inactive red dwarf star, which may increase the likelihood that this planet could potentially sustain life. Ross 128 b will be a prime target for ESO’s Extremely Large Telescope, which will be able to search for biomarkers in the planet’s atmosphere. [Larger image.]

A temperate Earth-sized planet has been discovered only 11 light-years from the Solar System by a team using ESO’s unique planet-hunting HARPS instrument. The new world has the designation Ross 128 b and is now the second-closest temperate planet to be detected after Proxima b. It is also the closest planet to be discovered orbiting an inactive red dwarf star, which may increase the likelihood that this planet could potentially sustain life. Ross 128 b will be a prime target for ESO’s Extremely Large Telescope, which will be able to search for biomarkers in the planet’s atmosphere.

A team working with ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile has found that the red dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Ross 128 is the “quietest” nearby star to host such a temperate exoplanet.

“This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations,”

explains Nicola Astudillo-Defru (Geneva Observatory – University of Geneva, Switzerland), who co-authored the discovery paper.

This image shows the sky around the red dwarf star Ross 128 in the constellation of Virgo (The Virgin). It was created from images forming part of the Digitized Sky Survey 2. Ross 128 appears at the centre of the picture. Close inspection reveals that Ross 128 has a strange multiple appearance as this image was created from photographs taken over a more than forty year period, and the star, which is only 11 light-years from Earth, moved across the sky significantly during this time. Ross 128 is a “quiet” red dwarf star and is orbited by Ross 128 b, an exoplanet with a similar mass and temperature to the Earth. [Larger images.]

Red dwarfs are some of the coolest, faintest — and most common — stars in the Universe. This makes them very good targets in the search for exoplanets and so they are increasingly being studied. In fact, lead author Xavier Bonfils (Institut de Planétologie et d’Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, Grenoble, France), named their HARPS programme The shortcut to happiness, as it is easier to detect small cool siblings of Earth around these stars, than around stars more similar to the Sun [1].

Many red dwarf stars, including Proxima Centauri, are subject to flares that occasionally bathe their orbiting planets in deadly ultraviolet and X-ray radiation. However, it seems that Ross 128 is a much quieter star, and so its planets may be the closest known comfortable abode for possible life.

Although it is currently 11 light-years from Earth, Ross 128 is moving towards us and is expected to become our nearest stellar neighbour in just 79 000 years — a blink of the eye in cosmic terms. Ross 128 b will by then take the crown from Proxima b and become the closest exoplanet to Earth!

With the data from HARPS, the team found that Ross 128 b orbits 20 times closer than the Earth orbits the Sun. Despite this proximity, Ross 128 b receives only 1.38 times more irradiation than the Earth. As a result, Ross 128 b’s equilibrium temperature is estimated to lie between -60 and 20°C, thanks to the cool and faint nature of its small red dwarf host star, which has just over half the surface temperature of the Sun. While the scientists involved in this discovery consider Ross 128b to be a temperate planet, uncertainty remains as to whether the planet lies inside, outside, or on the cusp of the habitable zone, where liquid water may exist on a planet’s surface [2].

Astronomers are now detecting more and more temperate exoplanets, and the next stage will be to study their atmospheres, composition and chemistry in more detail. Vitally, the detection of biomarkers such as oxygen in the very closest exoplanet atmospheres will be a huge next step, which ESO’s Extremely Large Telescope (ELT) is in prime position to take [3].

“New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterisation. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterise a large fraction of these planets,” concludes Xavier Bonfils.

Notes

[1] A planet orbiting close to a low-mass red dwarf star has a larger gravitational effect on the star than a similar planet orbiting further out from a more massive star like the Sun. As a result, this “reflex motion” velocity is much easier to spot. However, the fact that red dwarfs are fainter makes it harder to collect enough signal for the very precise measurements that are needed.

[2] The habitable zone is defined by the range of orbits around a star in which a planet can possess the appropriate temperature for liquid water to exist on the planet’s surface.

[3] This is only possible for the very few exoplanets that are close enough to the Earth to be angularly resolved from their stars.

Astronomy

Video: An astronomer learned “to hear the stars” after losing her eyesight

November 13, 2017 TopSpacer 1 Comment

An interesting story of an astronomer finding a way to continue her research after losing her eyesight: Wanda Diaz Merced: How a blind astronomer found a way to hear the stars | TED Talk

From the caption:

Wanda Diaz Merced studies the light emitted by gamma-ray bursts, the most energetic events in the universe. When she lost her sight and was left without a way to do her science, she had a revelatory insight: the light curves she could no longer see could be translated into sound. Through sonification, she regained mastery over her work, and now she’s advocating for a more inclusive scientific community. “Science is for everyone,” she says. “It has to be available to everyone, because we are all natural explorers.”

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Astronomy

ESO: Dust belt observed around Proxima Centauri, our nearest neighbor star

November 3, 2017 TopSpacer 1 Comment

A new ESO (European Southern Observatory) report:

ALMA Discovers Cold Dust Around Nearest Star

This artist’s impression shows how the newly discovered belts of dust around the closest star to the Solar System, Proxima Centauri, may look. ALMA observations revealed the glow coming from cold dust in a region between one to four times as far from Proxima Centauri as the Earth is from the Sun. The data also hint at the presence of an even cooler outer dust belt and indicate the presence of an elaborate planetary system. These structures are similar to the much larger belts in the Solar System and are also expected to be made from particles of rock and ice that failed to form planets. Note that this sketch is not to scale — to make Proxima b clearly visible it has been shown further from the star and larger than it is in reality. [ Larger images]

ALMA Observatory in Chile has detected dust around the closest star to the Solar System, Proxima Centauri. These new observations reveal the glow coming from cold dust in a region between one to four times as far from Proxima Centauri as the Earth is from the Sun. The data also hint at the presence of an even cooler outer dust belt and may indicate the presence of an elaborate planetary system. These structures are similar to the much larger belts in the Solar System and are also expected to be made from particles of rock and ice that failed to form planets.

Proxima Centauri is the closest star to the Sun. It is a faint red dwarf lying just four light-years away in the southern constellation of Centaurus (The Centaur). It is orbited by the Earth-sized temperate world Proxima b, discovered in 2016 and the closest planet to the Solar System. But there is more to this system than just a single planet. The new ALMA observations reveal emission from clouds of cold cosmic dust surrounding the star.

The lead author of the new study, Guillem Anglada [1], from the Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain, explains the significance of this find:

“The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”

Dust belts are the remains of material that did not form into larger bodies such as planets. The particles of rock and ice in these belts vary in size from the tiniest dust grain, smaller than a millimetre across, up to asteroid-like bodies many kilometres in diameter [2].

Dust appears to lie in a belt that extends a few hundred million kilometres from Proxima Centauri and has a total mass of about one hundredth of the Earth’s mass. This belt is estimated to have a temperature of about –230 degrees Celsius, as cold as that of the Kuiper Belt in the outer Solar System.

There are also hints in the ALMA data of another belt of even colder dust about ten times further out. If confirmed, the nature of an outer belt is intriguing, given its very cold environment far from a star that is cooler and fainter than the Sun. Both belts are much further from Proxima Centauri than the planet Proxima b, which orbits at just four million kilometres from its parent star [3].

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope. [Larger images]

Guillem Anglada explains the implications of the discovery:

“This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”

Proxima Centauri’s planetary system is also particularly interesting because there are plans — the Starshot project — for future direct exploration of the system with microprobes attached to laser-driven sails. A knowledge of the dust environment around the star is essential for planning such a mission.

This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The picture was created from pictures forming part of the Digitized Sky Survey 2. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in colour like the Sun. [Larger images]

Co-author Pedro Amado, also from the Instituto de Astrofísica de Andalucía, explains that this observation is just the start:

“These first results show that ALMA can detect dust structures orbiting around Proxima. Further observations will give us a more detailed picture of Proxima’s planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”

Notes

[1] In a cosmic coincidence, the lead author of the study, Guillem Anglada shares his name with the astronomer who led the team that discovered Proxima Centauri b, Guillem Anglada-Escudé, himself a co-author of the paper in which this research is published, although the two are not related.

[2] Proxima Centauri is quite an old star, of similar age to the Solar System. The dusty belts around it are probably similar to the residual dust in the Kuiper Belt and the asteroid belt in the Solar System and the dust that creates the Zodiacal Light. The spectacular discs that ALMA has imaged around much younger stars, such as HL Tauri, contain much more material that is in the process of forming planets.

[3] The apparent shape of the very faint outer belt, if confirmed, would give astronomers a way to estimate the inclination of the Proxima Centauri planetary system. It would appear elliptical due to the tilt of what is assumed to be in reality a circular ring. This would in turn allow a better determination of the mass of the Proxima b planet, which is currently known only as a lower limit.