Research Highlights

MaNGA reveals how galaxies stop forming stars

Our understanding of the galaxy populations at both low-z and high-z has advanced dramatically, thanks to the large photometric/spectroscopic surveys of galaxies accomplished in the past one and a half decades. It's well established that the galaxies can be divided into two major populations in the space of stellar mass (or luminosity) and color. In addition, the fraction of the red population has steadily increased by a factor of two since redshift of unity, indicating that the star formation cessation in galaxies has been an important process driving the galaxy evolution in the past ~80 Gyr. However, how the star formation gets shutdown and what processes drive the star formation cessation are not fully understood. Processes internal to individual galaxies (e.g. secular evolution driven by bars or minor mergers, AGN feedback, etc.) and external environmental effects (e.g. tidal stripping and ram-pressure stripping) are both believed to play important roles. Therefore, in order to have a complete picture of the star formation cessation, one would need to have deep imaging and spatially resolved spectroscopy for a large sample of galaxies covering wide ranges of galaxy properties and environment. Such samples have become available only recently from the integral field spectroscopy (IFS) surveys.


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THCA AST3-2 telescope observes GW170817's optical counterpart

On August 17, 2017, the now famous LIGO gravitational wave detector and VIRGO, the italo-french detector simultaneously observed a gravitational wave signal (GW170817). The joint detection allowed a more precise positioning of the event, located at about 130 million light years in a 31 square degrees area. This precision, which was not possible with LIGO-only observations allowed more than 70 observatories and telescopes in the world to point to the position in a most exciting and beautifully orchestrated series of multi-band follow-up observations of the electromagnetic signals associated to a gravitational event. This is the first ever observed neutron star collision, and it is in both gravitational waves and its electromagnetic counterparts (from high energy gamma-rays, X-rays, optical, and radio wavelengths) and will be certainly remembered as the start of gravitational waves astronomy.

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THCA members participate in Insight-HXMT obs of GW170817

On Oct. 16th 2017 Beijing Time, the National Science Foundation of the United States (NSF) announced at a news conference the discovery of a binary neutron star coalescence event (designated GW170817) through gravitational waves detected by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) together with the Advanced Virgo interferometer. This historic event triggered a rare, global joint observational campaign with dozens of astronomical equipment at all wavelengths in search of the elusive electromagnetic counterparts. Insight-HXMT, the first X-ray Satellite of China launched on Jun. 15th 2017, which is still under test, observed GW170817.


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THCA Professor publishes a review paper in ARA&A

On August 18, 2017, a review paper entitled Ultraluminous X-ray Sources was published in this year’s Annual Review of Astronomy and Astrophysics, written by THCA Professor Hua Feng (second author), in collaboration with Philip Kaaret (first author), and Tim Roberts. The paper reviews the observational facts of a special kind of X-ray sources in the sky, so-called ultra-luminous X-ray sources (ULXs), and how theoretical models and numerical simulations can explain the data. The link between the studies of ULXs, the early universe, and the detection of gravitational waves is also discussed. Prof. Feng’s major interests are 1) to understand the physics around compact objects, including ULXs and 2) to develop novel instrumentation for future X-ray astronomy.

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Free-floating planets not as common as thought?

More than 3500 extrasolar planets have now been detected; the study of these extrasolar planets and our own solar system is one of the most exciting areas in astrophysics. Virtually all of these planets are found around other stars. For example, our Earth orbits around the Sun. However, theory predicts some planets are either formed or ejected from proto-planetary disks because of dynamical interactions during their formation. These planets are called free-floating or rogue planets (see the cover illustration).

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