Astronomy Graduate Student Receives Publication Award

  PhD student Junghwan Oh     The Korean Astronomical Society (KAS) [http://www.kas.org/] has awarded its 2016 Rising Star Award to Oh Junghwan, a PhD student in the SNU Astronomy Program working in the group of Prof. Sascha Trippe.   The Rising Star Award recognizes outstanding scientific publications in Korean astronomy journals by students.   Oh Junghwan works on radio astronomical observations of active galactic nuclei (AGN), the luminous centers of galaxies powered by accretion of gas into supermassive black holes. In 2015, he published an analysis based on data from the Korean-Japanese KaVA radio array [http://radio.kasi.re.kr/kava/main_kava.php] that traced the motion of AGN jets over time. For two sources they were able to show that the jets are moving at about 98% of the speed of light and are pointed into the direction of Earth.   This study, which has now been found price-worthy by the KAS, was published in the Journal of the Korean Astronomical Society [http://jkas.kas.org/].   The Rising Star Award is going to be handed over during the Spring Meeting of the KAS on April 13 and 14, 2016, in Busan.   Reference: Oh, J., et al. 2015, JKAS, 48, 299 [http://jkas.kas.org/journals/2015v48n5/v48n5p299_trippe2.pdf]

2016-04-08

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Scientists to Provide Update On the Search for Gravitational Waves

          MEDIA ADVISORY   For Immediate Release:Monday, February 8, 2016   THURSDAY: SCIENTISTSTO PROVIDE UPDATE ON THE SEARCH FOR GRAVITATIONAL WAVES       100 years after Einsteinpredicted the existence of gravitational waves, the National Science Foundationgathers scientists from Caltech, MIT and the LIGO Scientific Collaboration toupdate the scientific community on efforts to detect them.   (Washington, DC) --Journalists are invited to join the National Science Foundation as it bringstogether the scientists from Caltech, MIT and the LIGO Scientific Collaboration(LSC) this Thursday at 10:30 a.m. at the National Press Club for a statusreport on the effort to detect gravitational waves - or ripples in the fabricof spacetime - using the Laser Interferometer Gravitational-wave Observatory(LIGO).    This year marks the 100thanniversary of the first publication of Albert Einstein's prediction of theexistence of gravitational waves. With interest in this topic piqued by thecentennial, the group will discuss their ongoing efforts to observegravitational waves.    LIGO, a system of twoidentical detectors carefully constructed to detect incredibly tiny vibrationsfrom passing gravitational waves, was conceived and built by MIT and Caltechresearchers, funded by the National Science Foundation, with significantcontributions from other U.S. and international partners. The twin detectorsare located in Livingston, Louisiana, and Hanford, Washington. Research and analysisof data from the detectors is carried out by a global group of scientists,including the LSC, which includes the GEO600 Collaboration, and the VIRGOCollaboration.    For additional backgroundabout the project, you may be interested in these websites:      ·LIGO Lab: https://ligo.caltech.edu/ (Observatories: Livingston | Hanford )  ·Advanced LIGO: https://www.advancedligo.mit.edu/ ·LIGO Scientific Collaboration: http://www.ligo.org/ ·LIGO Partner Experiments and Collaborations: http://www.ligo.org/partners.php    WHEN:                                                                                  Thursday, Feb. 11, 2016 10:30 AM US EST    WHERE:  The National Press Club Holeman Lounge 529 14th Street NW, 13th Floor Washington, DC 20045    MEDIA RSVP:  Seating is extremelylimited, but an overflow room will be available where reporters can still askquestions and have access to additional subject matters to interview after thepress conference. Only the first 50 journalists to arrive will be seated in themain room. All interested journalists should RSVP to any of the media contactslisted below to ensure press credentials are prepared ahead of time. A mult boxwill be available for broadcast media, and the Press Club is equipped withwireless access.    LIVE WEBCAST:  For press not based in theWashington, D.C. area, this event will be simulcast live online, and we willtry to answer some questions submitted remotely. For details about how toparticipate remotely, please contact anyone listed below.    MEDIA CONTACTS:  Caltech/Tom Waldman, (626) 395-5832 or (818)274-2729 [m]; twaldman@caltech.edu MIT/Kimberly Allen, (617) 253-2702 or (617) 852-6094 [m]; allenkc@mit.edu NSF/Ivy Kupec, (703) 292-8796 or (703) 225-8216 [m]; ikupec@nsf.gov   

2016-02-11

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Dr. Hyunsung Jun wins 2015 JPL Outstanding Postdoctoral Research Awards

Dr. Hyunsung Jun (advisor: Prof. Myungshin Im) was awarded 2015 JPL Outstanding Postdoctoral Research Awards.        JPL Chief Scientist Dan McCleese, Hyunsung Jun, JPL Director Charles Elachi   http://scienceandtechnology.jpl.nasa.gov/newsandevents/newsdetails/?NewsID=3464 https://www.facebook.com/jplpdocs/photos/a.10154234165105550.1073741828.358402695549/10154343390920550/ https://www.facebook.com/jplpdocs/photos/a.10154234165105550.1073741828.358402695549/10154343391545550/ https://www.facebook.com/jplpdocs/photos/a.10154234165105550.1073741828.358402695549/10154343391975550/

2015-12-03

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The gas streams from supermassive black holes

         Prof. Sascha Trippe  PhD student Jae-Young Kim PhD student Junghwan Oh PhD student Taeseok Lee   Active galactic nuclei (AGN) are the strongest sources of energy in the universe, being up to 10,000 times brighter than our home galaxy, the Milky Way. They are powered by accretion of interstellar gas into supermassive black holes located in the centers of galaxies; each of those black holes has a mass of a few million to a few billion times the mass of the sun. Some AGN emit "jets", streams of gas up to several million light years long. To date, the physics behind the formation of these jets is not understood.   A team of SNU astronomers led by Prof. Sascha Trippe used the Korean VLBI Network (KVN) and the Korean-Japanese KVN and VERA Array (KaVA) for a detailed study of the physics of AGN jets. Their Plasma-physics of Active Galactic Nuclei (PAGaN) project was conducted in collaboration with radio astronomers at KASI. First results have now been published in a series of articles in a special issue of the Journal of the Korean Astronomical Society (JKAS).   The first publication, led by SNU graduate student Jae-Young Kim (now a PhD student at the Max Planck Institute for Radio Astronomy in Bonn, Germany) analyzed the light from six bright AGN. Their results show that AGN jets are highly turbulent, leading to characteristic signatures in the polarized radiation from their targets.   The second paper, led by SNU graduate student Junghwan Oh, used data from the KaVA array to trace the motion of AGN jets over time. For two sources they were able to show that the jets are moving at about 98% of the speed of light and are pointed into the direction of Earth.   The third publication, led by SNU graduate student Taeseok Lee, presents a search for very fast ("intra-day") variations in the brightness of four AGN with the KVN. Their statistical analysis showed no variations on time scales from minutes to hours, in agreement with theoretical limits.   < REFERENCES > “PAGAN I: MULTI-FREQUENCY POLARIMETRY OF AGN JETS WITH KVN”, Kim, J.-Y., et al. 2015, JKAS, 48, 285 “PAGAN II: THE EVOLUTION OF AGN JETS ON SUB-PARSEC SCALES”, Oh, J., et al. 2015, JKAS, 48, 299 “A SEARCH FOR AGN INTRA-DAY VARIABILITY WITH KVN”, Lee, T., et al. 2015, JKAS, 48, 313       Figure 1 False color composite of the active galaxy Centaurus A. The optical image shows the  elliptical galaxy itself. X-ray and radio images show jets and high-energy gas outflows. [Image credit: NASA/ESO/CXC/VLA/R.Kraft et al./M. Hardcastle et al./M. Rejkuba et al.]     Figure 2 The jet of 3C 111 observed with KVN at 22 GHz (left) and 43 GHz(right). Each panel shows the motions (toward the left) of individual jet components (connected with dotted lines) over time lines of 161 and 384 days, respectively. The apparent jet speed is up to five times the speed of light. Red arrows mark a new component that appeared after the beginning of the observations. [Image credit: Oh et al.2015]  

2015-11-24

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Discovery of a Faint Quasar at z=6: Illumination of the Early Universe by Quasars

Discovery of a Faint Quasar at z=6: Illumination of the Early Universe by Quasars     A team of Korean astronomers discovered a faint quasar in the early Universe which sheds light on the main sources of illumination about 1 billion years after the Big Bang. The team used the Gemini South telescope in Chile, and several telescopes on Maunakea in Hawai‘i, to make the discovery. This is the first published scientific result from the Korean astronomical community since the Korea Astronomy and Space Science Institute (KASI) joined in a limited partnership with Gemini at the beginning of 2015.     The history of objects we see today in the Universe started when the first stars formed a few hundred million years after the Big Bang. However, it has been unclear what types of objects illuminated the intergalactic medium in order to ionize neutral atoms (called the re-ionization of the universe).     Quasars, because they are so bright, have been suggested as one of the main “culprits” for the source of re-ionizing energy. Quasars shine when supermassive black holes at the centers of galaxies vigorously accrete gas and stars – they can blaze at up to 100 times the total brightness of their host galaxies. Knowing the number of quasars in the early Universe with moderate luminosity (from about a few to 10 times more luminous than our Milky Way galaxy) can provide an important clue to solving this puzzle, since moderate luminosity quasars dominate the available illumination provided by quasars.     However, moderate luminosity quasars are faint (because they are so distant), and rare, so it is challenging to find them. So far, only two or three such objects have been identified. In order to find moderate luminosity quasars at a redshift of 6 (or about one billion years after the Big Bang), the team performed a moderately wide and deep imaging survey, called the Infrared Medium-deep Survey (IMS) using the data taken with telescopes on Maunakea, including the United Kingdom Infrared Telescope, and the Canada-France-Hawai‘i Telescope. In a subset of these data, the team identified 7 faint quasar candidates. Subsequently, the spectrum of one of these quasars, obtained with the Gemini Multi-Object Spectrograph (GMOS) at the Gemini South telescope in July 2015, revealed that the object is indeed a much sought-after moderate luminosity quasar in the early Universe.        Figure 1. Color composite-image of IMS J2204+0111 at z=6 (about 1 billion years after the Big Bang). IMS J2204+0111 is the red object at the center and its distance from us is 12.8 billion light years. Because of the expansion of the universe, distant objects like IMS J2204+0111 move away from us almost at the speed of the light, making their light to shift into near-infrared wavelength (phenomenon, called “redshift”). This makes them look very red in comparison to other objects, and this special color feature enabled the team to identify distant quasar candidates.        The newly discovered quasar, named as IMS J220417.92+011144.8, is expected to harbor a black hole of about 10 million to 100 million solar masses. Its distance is about 12.8 billion light-years from us. The discovery of IMS J2204+0111 and the statistical results of the survey suggest that quasars can only contribute up to about 10% of the re-ionizing flux in the early Universe. This value is lower than expected and doesn’t provide enough energy to fully account for the re-ionization of the Universe. Additionally, the redshifts of the other quasar candidates are still unknown; if they turn out not to be quasars, this number would be reduced even further. Therefore, it is unlikely that quasars are the dominant sources of illumination in the early Universe: 90% or more of the light must originate from other objects.      Figure 2: GMOS spectrum of IMS J2204+0111. A prominent break in the spectrum is visible at the wavelength of about 8500 Å. The feature corresponds to the Hydrogen Lyman-α line which has a wavelength of 1216 Å at rest. It is now shifted to 8500 Å, suggesting that this object is moving away from us at the redshift of 5.944. The sharp break is caused because neutral hydrogen around the quasar absorbed the light at the wavelength below the Lyman-α line.       The discovery was made possible thanks to the GMOS’s high sensitivity to infrared light where most of the light of such high-redshift quasars is concentrated. This work was carried out by Yongjung Kim (lead author), Myungshin Im (Principal Investigator), and Yiseul Jeon of Seoul National University, Minjin Kim at Korea Astronomy and Space Science Institute, and 14 other collaborators. The result was published in the November 10 issue of The Astrophysical Journal Letters, and the paper is available on the astro-ph.     ■ Gemini Observatory   http://www.gemini.edu/node/12446

2015-11-12

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