Friday, March 6, 2020

Where there's one, there's one hundred more

Although it may have a difficult designation to remember, PSO J030947.49+271757.31, its importance is unique.  It is the most distant Blazar observed to date.  The light we see from it began its journey when the Universe was less than 1 billion years old, almost 13 billion years ago

PSO J0309 + 27 – in short - was discovered by a team of researchers led by Silvia Belladitta, a PhD student at the University of Insubria, working for the Italian National Institute for Astrophysics (INAF) in Milan, under the supervision of Alberto Moretti and Alessandro Caccianiga. While it was suspected that the object was distant, and observations from the Swift Space Telescope (of which INAF is a major contributor) showed its X-ray power matched that of other Blazars, it was the observations obtained with the optical Multi-Double Object Spectrographs (MODS) at the Large Binocular Telescope (LBT) that confirmed it indeed broke the record as the most distant Blazar in the known Universe. 

Blazars are one of the brightest of a class of objects called AGN - or Active Galactic Nuclei - which are supermassive black holes (SMBHs) in the centers of galaxies.  They are active due to the presence of a disk or sphere of ionized gas around them which "fuels" the emission seen at many wavelengths.  Blazars emit powerful relativistic jets bright enough to be seen across the known Universe.  The beam of a Blazar is only visible along a narrow line of sight.  If the Earth is not within that line of sight, it would not be easily recognizable. Thus detecting objects can be extremely difficult (and fortuitous).  But more importantly, this Blazar is one of the earliest, most distant SMBHs seen that is not obscured by dust (unlike most AGN). This allows astronomers to study this object across the entire electromagnetic spectrum and build a complete picture of its properties.

"The spectrum that appeared before our eyes confirmed first that PSO J0309 + 27 is actually an AGN, or a galaxy whose central nucleus is extremely bright due to the presence, in its center, of a supermassive black hole fed by the gas and the stars it engulfs, ”says Belladitta. "In addition, the data obtained by LBT also confirmed that PSO J0309 + 27 is really far away from us using the shift of the color of its light towards red or redshift with a record value of 6.1, never measured before for a similar object," adds Belladitta, first author of the paper describing the discovery, published today in the journal Astronomy & Astrophysics Letters.

PSO J0309 + 27 has therefore proved to be, at the moment, the most powerful persistent radio source in the primordial universe, within the first billion years since its formation. Observations taken by the XRT telescope on board the Swift satellite - a mission with a fundamental contribution by INAF and the Italian Space Agency - have also made it possible to establish that, even in X-rays, PSO J0309 + 27 is the brightest cosmic source ever observed at these distances.

MODS/LBT discovery spectrum of PSO J0309+27 at z=6.10±0.03. The O[VI]λ1033Å, the Ly-αλ1216Å the OIλ1304Å and the CIIλ1336Å lines are marked. The red-dashed line is the quasar template from Vanden Berk et al. (2001) at the redshift of the object for comparison.
Belladitta notes further,  “Observing a blazar is extremely important, for every discovered source of this type, we know that there must be a hundred similar, but oriented differently and therefore too weak to be seen directly". Therefore, the discovery of PSO J0309 + 27 allows astronomers to quantify, for the first time the number of AGN with powerful relativistic jets present in the primordial universe. The Blazars at these early epochs represent the "seeds" for all SMBHs that exist in the Universe today.

“From these new LBT observations, still under development, we also estimate that the central engine that powers PSO J0309 + 27 is a black hole with a mass equal to about a billion times the mass of our Sun. Thanks to our discovery, we are able to say that already in the first billion years of life of the universe, there existed a large number of very massive black holes emitting powerful relativistic jets. This result places tight constraints on the theoretical models that try to explain the origin of these huge black holes in our universe" concludes Belladitta.

Science contact     Silvia Belladitta    silvia.belladitta@inaf.it
Media contact at INAF (Italy)        ufficiostampa@inaf.it
Media contact at LBT (Arizona)    pr_officer@lbto.org

INAF press release: https://www.media.inaf.it/2020/03/06/blazar-da-record/

Publication:
S. Belladitta, A. Moretti, A. Caccianiga, C. Spingola, P. Severgnini, R. Della Ceca, G. Ghisellini, D. Dallacasa, T. Sbarrato, C. Cicone, L. P. Cassarà,  and M. Pedani.    link to the pdf version
A&A 635, L7 (2020) 

Monday, March 2, 2020

Total lunar eclipse: observing the Earth as a transiting planet

Astronomers succeeded in recording sunlight shining through the Earth’s atmosphere in a manner similar to the study of distant exoplanets. During the extraordinary occasion of a lunar eclipse, the Large Binocular Telescope observed the light that was filtered by the Earth’s atmosphere and reflected by the Moon in unique detail. In addition to oxygen and water, atomic spectral lines of sodium, calcium and potassium were detected in our atmosphere in this way first time.

Total lunar eclipse: observing the Earth as a transiting planet
The Sun as seen from the Tycho crater on the Moon during a total lunar eclipse on Earth. When the Sun sets behind the northern Pacific, its disk completely disappears behind Earth. Credit: AIP/Strassmeier/Fohlmeister
When an exoplanet transits in front of its host star, astronomers may be able to record both the dimming of the starlight that the planet blocks and also the starlight that shines through the planet’s atmosphere. While it is only a tiny signal, it contains the imprint of the planet’s chemical and physical signature and provides the principal possibility to measure the planet’s atmospheric constituents. In astrophysics, this technique is called transmission spectroscopy, and is a relatively young technique booming since many exoplanet transits were detected from space. “While, so far, only applicable to super-sized Jupiters, that is oversized Jupiter-like planets orbiting close to their host star, we are most interested in Earth-like planets and whether we could detect more complex molecular signatures in an exo-Earth transmission spectrum possibly even hinting for life”, explains Klaus Strassmeier from the Leibniz Institute for Astrophysics in Potsdam (AIP), the leading author of the now published study. „While not yet doable for any Earth-like exoplanet transit, a total lunar eclipse, which is a total solar eclipse when seen from our own Moon, is nothing else than a transit of our own Earth, and indirectly observable.”

The sunlight that passes through the Earth’s atmosphere before it reaches the Moon and back reflects to Earth is called the Earthshine. The Earth’s atmosphere contains many by-products of biological activity, such as oxygen and ozone in association with water vapor, methane and carbon dioxide. These biogenic molecules present attractive narrow molecular bands at optical and near infrared wavelengths for detection in atmospheres of other planets. Taking the Earth as the prototype of a habitable planet, Earthshine observations provide the possibility to verify biogenic and related chemical elemental presence with the same techniques that otherwise are being used for observing stars with super Jupiter planets. Earthshine is thus an ideal test case for future exo-Earth detections with the new generation of extremely large telescopes.

January 2019 featured a total lunar eclipse. The Moon dimmed by a factor of 20,000 during totality which is the reason why the light gathering capability of the 11.8 m Large Binocular Telescope (LBT) in Arizona was needed for the observations. Additionally, the high spectral resolution of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) was necessary to separate the expected tiny spectral-line absorptions of the Earth’s atmosphere from the normal solar spectrum at unprecedented spectral resolution and in polarized light.

“PEPSI has already made significant contributions to the study of exoplanets through the observation of their transit in front of their sun.” adds Christian Veillet, LBT Observatory's Director. “Looking at the Earth as an exoplanet thanks to a total lunar eclipse well-suited to LBT's location in Arizona, and adding polarimetry to the exquisite resolution of the PEPSI spectrograph, resulted in the detection of sodium, calcium, and potassium in Earth's atmosphere."
Snapshot spectra of terrestrial molecular oxygen and water vapor absorption. Intensity is plotted versus wavelength in Angstroem. Time increases from bottom up as indicated in UT hh:mm:ss. Immediately noticeable is the dramatic increase of O2 and H2O absorption during eclipse (central four spectra) with respect to outside eclipse (other spectra). Oxygen molecules create the so-called A-band at 7600 Å, H2O is seen as myriads of individual absorption lines in the range 7850–9100 Å. Credit: AIP/Strassmeier. 
Detailed look at the wavelengths around the potassium line at 7699 Å. Time increases bottom up and is again indicated as UT. The bottom spectrum is a comparison spectrum of the full moon outside of eclipse. Red color denotes times of totality, black times of partiality, and blue out of eclipse. Note that the spectral lines flanking the potassium line are from two terrestrial water vapor absorptions. Credit: AIP/Strassmeier.



More information on PEPSI and the LBT: https://pepsi.aip.de | http://www.lbto.org


Science contact: 
        Prof. Dr. Klaus G. Strassmeier, 0331-7499-223, kstrassmeier@aip.de

Media contacts: 
        Dr. Janine Fohlmeister (Potsdam, Germany)  0331-7499-803, presse@aip.de
        Dr. Christian Veillet (Tucson, USA)   1-520-349-4576, pr_officer@lbto.org



Publication:

Klaus G. Strassmeier, Ilya Ilyin, Engin Keles, Matthias Mallonn, Arto Järvinen, Michael Weber, Felix Mackebrandt, and John M. Hill, 2020, Astronomy & Astrophysics, in press


Friday, September 27, 2019

Found: Three Black Holes on Collision Course


A team of astronomers, led by Graduate Student Ryan Pfeifle of George Mason University (GMU) in Fairfax Virginia, used observations spanning the electro-magnetic spectrum to provide the strongest evidence to-date of the existence of three Active Galactic Nuclei (AGN) residing in a merging galaxy.  

Beginning with a sample of hundreds of likely merging galaxies identified by the Galaxy Zoo Citizen Science Program and using thermal infrared observations from NASA's Wide-field Infrared Survey Explorer (WISE), Pfeifle and his team identified a few dozen candidate systems which were thought to host two Active Galactic Nuclei (AGN).   AGN are supermassive black holes at least 1 million times more massive than our Sun which are energized by the presence of vast quantities of gas drawn into them by gravitational forces. 

Space-based X-ray observations obtained with the Chandra Observatory Nuclear Spectroscopic Telescope Array (NuStar) found evidence to support the presence of two AGN in most of the merging galaxies.  However, one system appeared to be significantly more unusual than the rest, SDSS J084905.51+111447.2 (shortened to SDSS J0849+1114). Here, the team found X-ray evidence to suggest three AGN resided in this merging galaxy.

In order to provide more definitive support, and rule out competing astrophysical explanations, the team turned to the Large Binocular Telescope Observatory (LBT), currently the world's largest optical/infrared telescope.  Led by Dr. Barry Rothberg, who is a staff astronomer at LBT and holds a concurrent affiliate faculty position at GMU, optical and infrared spectroscopic observations of SDSS J0849+1114 were obtained using the Multi-Object Double Spectrographs (MODS), and the LBT Utility Camera in the Infrared (LUCIs).

The spectroscopic observations allow optical and near-infrared light to be separated so that atomic and molecular species can be identified.  The MODS and LUCI LBT observations conclusively demonstrated the presence of atomic species which can only exist in conditions found in AGN, as well as the presence of fast flowing gas that could only be powered by these monsters.  Moreover, the spectroscopic data allowed the team to determine the ages of the stars in the host galaxy, further ruling out competing astrophysical explanations for the presence of the three X-ray detections.  

Recent work by the team has expanded their study of this object to radio wavelengths.  "The use of multi-wavelength space- and ground-based observatories shows the synergies needed to discover such unusual, but important astrophysical phenomenon.  There is no way we could have confirmed the existence of a Triple AGN without contributions from all of these observatories," says Dr Rothberg.

However, the team's work is far from finished.  Pfiefile notes that the team's new multi-wavelength technique will allow them to extend their work to finding more triples.  "We already have more candidates that we are actively pursuing. I look forward to LBT once again demonstrating its importance in finding the optical and near-infrared signatures that either confirm or reject the presence of AGN in merging galaxies."


More details on the findings here with pictures and videos here.




Wednesday, September 4, 2019

Chemical element potassium detected in an exoplanet atmosphere

A team of astronomers led by AIP PhD student Engin Keles detected the chemical element potassium in the atmosphere of an exoplanet, for the first time with overwhelming significance and applying high-resolution spectroscopy. The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona was used to study the atmosphere on the Jupiter-like exoplanet HD189733b. 

Ever since the earliest theoretical predictions 20 years ago, the chemical elements potassium and sodium were expected to be detectable in atmospheres of “hot jupiters”, gaseous planets with temperatures of a few thousand Kelvin that orbit closely around far-away stars. While sodium was detected with high resolution observations already early on, potassium was not, which created a puzzle for atmospheric chemistry and physics.

The elements can be discovered by analyzing the home star’s spectrum of light when the planet passes in front of it as seen from Earth. Different elements cause specific absorption signals in the spectrum, dark lines, that hint at the chemical composition of the atmosphere. However, the presence of clouds in hot Jupiter atmospheres strongly weakens any spectral absorption features and thus makes them very hard to detect. Even for HD189733b, the best studied hot Jupiter, so far scientists only possessed a very vague and imprecise knowledge of the potassium absorption. The exoplanet, 64 light years away and about the size of Jupiter, orbits its home star – an active K dwarf – in 53 hours and is 30 times closer to it than the Earth to the Sun. It needed the light gathering capability of the 2x8,4m LBT and the high spectral resolution of PEPSI to definitely measure potassium for the first time at high resolution in atmospheric layers above the clouds. With these new measurements, researchers can now compare the absorption signals of potassium and sodium and thus learn more about processes such as condensation or photo-ionization in these exoplanet atmospheres.

Potassium detection in HD189733b. The figure depitcts the excess absorption in the potassium line in the expoplanet’s atmosphere during transit. The horizontal axis shows the time in minutes, 0 means the exoplanet is at the central meridian near the middle of the stellar disk.  Vertical dashed lines indicate the transit duration. The blue line shows the modelled planetary absorption. Credit: AIP/Engin Keles, Kristin Riebe


The technique that was applied for this study at LBT is called transmission spectroscopy. It requires that the exoplanet transits in front of the host star. “We took a time series of light spectra during the transit and compared the absorption depth,” says the lead author of the study, Engin Keles, PhD student at AIP in the group Stellar Physics and Exoplanets. “During transit, we then detected the potassium signature, which disappeared before and after transit as expected, which indicates that the absorption is induced by the planetary atmosphere.” Investigations by other teams already attempted to detect potassium on the same exoplanet, however, either nothing was found or what was found was too weak to be statistically significant. Until now there has been no significant detection of potassium in high resolution observations for any exoplanet. 

“Our observations clearly made the breakthrough” emphasizes project co-leader Dr. Matthias Mallonn, who is seconded by PEPSI’s principal investigator Prof. Klaus Strassmeier:  “PEPSI is well suited for this task because of its high spectral resolution that allows collecting more photons per pixel from very narrow spectral lines than any other telescope-spectrograph combination.” “Both as a spectrograph and as a spectropolarimeter, PEPSI has already made significant contributions to stellar physics,” adds Christian Veillet, LBT Observatory's Director. “This strong detection of potassium in the atmosphere of an exoplanet establishes PEPSI as an amazing tool for exoplanet characterization as well as a unique asset for the members of the LBT community.” The team included colleagues from Denmark, The Netherlands, Switzerland, Italy and the United States and has now presented the results in the journal Monthly Notices of the Royal Astronomical Society.



Original Publication Engin Keles, Matthias Mallonn, Carolina von Essen, Thorsten A. Carroll, Xanthippi Alexoudi, Lorenzo Pino, Ilya Ilyin, Katja Poppenhager, Daniel Kitzmann, Valerio Nascimbeni, Jake D. Turner, Klaus G. Strassmeier (2019), MNRAS, “The potassium absorption on HD189733b and HD209458b” https://doi.org/10.1093/mnrasl/slz123


Science contacts
At AIP (Potsdam, Germany)    Engin Keles, 0331-7499-538, ekeles@aip.de
                                                 Prof. Dr. Klaus G. Strassmeier, 0331-7499-223, kstrassmeier@aip.de
Aty LBTO (Tucson, USA)       Dr. Christian Veillet, 1 (520) 349-4576, cveillet@lbto.org


Monday, March 18, 2019

Mapping Stars with PEPSI



The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a so-called Zeeman-Doppler-Image (ZDI) of the surface of the magnetically active star II Pegasi. 

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes and interferometers. This technique, referred to as Doppler imaging (DI) or Doppler tomography, requires a high-resolution spectrograph, usually a large telescope, lots of observing time, and nifty analysis software.

But PEPSI can go a major step further. Because its two polarimeters also feed polarized light to the spectrograph, PEPSI captures the otherwise hidden profile deformation due to the Zeeman-effect. (splitting and polarization of spectral lines due to an external magnetic field). Combined with the rotational Doppler-effect it allows the reconstruction of the star’s surface magnetic field geometry. 

Stellar environment of the star II Pegasi. Shown is the magnetic-field extrapolation out to 2.2 stellar radii. Open field lines are depicted in colour (magenta: negative polarity, green: positive polarity, closed loops are in white.) Credit: AIP

Wednesday, April 25, 2018

Stellar Dust Survey Paves Way for Exoplanet Missions


Credits: NASA/JPL-Caltech
Using the Large Binocular Telescope Interferometer, or LBTI, on Mount Graham in Arizona, the HOSTS survey determines the brightness of warm dust floating in the orbital planes of other stars (called exozodiacal dust). In particular, HOSTS has studied dust in nearby stars’ habitable zones, where liquid water could exist on the surface of a planet. The LBTI is five to 10 times more sensitive than the previous telescope capable of detecting exozodiacal dust, the Keck Interferometer Nuller.

Among the findings detailed in the new paper, the HOSTS scientists report that a majority of Sun-like stars in their survey do not possess high levels of dust -- good news for future efforts to study potentially-habitable planets around those stars. A final report on the full HOSTS survey results is expected early next year.

More information about the new findings from HOSTS and the search for Earthlike planets beyond our solar system is available in this news release from the University of Arizona.

The full NASA Press Release is here.

Wednesday, January 10, 2018

First PEPSI Data Release



The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first batch of high-spectral resolution data to the scientific community. In a series of three papers in the European journal Astronomy & Astrophysics, the PEPSI team presents a new spectral atlas of the Sun, a total of 48 atlases of bright benchmark stars, and a detailed analysis of the chemical abundances of the 10-billion year old planet-system host Kepler-444.


Spectral atlases are the fingerprints of stars and give insights into almost all of their physical properties like temperature, pressure, velocities and chemical composition. The first paper contains a new spectral atlas of the Sun and proves for the first time that a night-telescope instrument can reach a quality comparable to a specialized solar instrument. All solar and stellar spectra were taken with an unprecedented spectral resolution of λ/Δλ=250,000, a resolution equivalent to a 1/100th of the diameter of a hydrogen atom (λ being the wavelength and Δλ the smallest measurable separation of two wavelengths) and cover the entire optical and near-infrared light (from 383 to 914nm).
The fingerprint of a star.
Example from the new PEPSI atlases:
the nearby planet-host star epsilon Eridani.
Click here for a full resolution pdf version.

For the Sun several spectral time series with up to 300 individual spectra per day were pre-analyzed and are also provided to the community. "These data recover the well-known solar 5-minute oscillation at a peak of 3 mHz (5.5min) from the disk-averaged light with a radial-velocity amplitude of only 47 cm/s, an incredibly small velocity from a stellar point of view", says Prof. Strassmeier, PEPSI principal investigator and director of the Cosmic Magnetic Field branch at the Leibniz Institute for Astrophysics Potsdam (AIP). The new atlas was also used to re-determine the abundance of Lithium in the Sun with very high precision. "Lithium is a key element for the nucleosynthesis in the universe and is also a tracer of mixing processes inside stars", explains Dr. Matthias Steffen, one of the project scientists. Three-dimensional dynamic model atmospheres and a full statistical treatment of the spectral properties of the lithium atom were applied to determine the solar abundance.

The 48 stellar atlases in the second paper include the northern Gaia benchmark stars as well as other Morgan-Keenan standard stars. Spectra of these targets were not available at the given resolution and signal-to-noise ratio (S/N) before. The latter quantity represents the photon noise relative to the signal strength from the star and thus the quality of the spectra. Previously available S/N for work on astrophysical parameters was typically several hundred at a spectral resolution λ/Δλ of at most 100,000. "PEPSI and the LBT provide S/N of several thousand at on average three times higher spectral resolution", says Ilya Ilyin, PEPSI’s project scientist. "With such numbers we have now the typical daytime solar-like spectrum quality available also for bright stars at night time", adds Strassmeier.

The PEPSI instrument at LBT. Credit: AIP
Finally, in the third paper, the star "Kepler-444", hosting five sub-terrestrial planets, was confirmed to be 10.5 billion years old, more than twice the age of our Sun and just a little bit younger than the universe as a whole. The star is also found being poor on metals. The chemical abundance pattern from the PEPSI spectrum indicates an unusually small iron-core mass fraction of 24% for its planets if star and planets were formed together. For comparison, terrestrial planets in the solar system have typically a 30% iron-core mass fraction. “This indicates that planets around metal-poor host stars are less dense than rocky planets of comparable size around more metal-rich host stars like the Sun”, explains Claude “Trey” Mack, project scientist for the Kepler-444 observation.


Science contacts:
    Prof. Dr. Klaus G. Strassmeier, 0331-7499-223, kstrassmeier@aip.de    
    Dr. Ilya Ilyin, 0331-7499-269, ilyin@aip.de
    Dr. Christian Veillet (Large Binocular Telescope Observatory), +1 (520) 621-5286, cveillet@lbto.org

Media contact:
    Dr. Janine Fohlmeister, 0331-7499-803, presse@aip.de

More information on PEPSI and the LBT:
    https://pepsi.aip.de/
    http://www.lbto.org/