Stars

Diagram of Earth as a detection center for very low-frequency gravitational waves emitted by pairs of supermassive black holes (top) using pulsars (bottom) (Image courtesy EPTA)

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A series of articles published or being published in the journals “Astronomy and Astrophysics” and “The Astrophysical Journal Letters” reports various aspects of the detection of very low-frequency gravitational waves. Researchers from the European Pulsar Timing Array (EPTA), the Indian Pulsar Timing Array (InPta), the Parkes Pulsar Timing Array (PPTA), the Chinese Pulsar Timing Array (CPTA), and the North American Nanohertz Observatory for Gravitational Waves (NanoGrav) analyzed data collected over the course of more than 25 years using groups of pulsars to obtain a kind of detector of gravitational waves at the galactic level. This was possible by exploiting the extreme regularity of the signals emitted by pulsars to detect variations of less than a millionth of a second and their correlations to identify gravitational waves. This technique expands the gravitational-wave astronomy opened up by the LIGO and Virgo detectors since the announcement of the first detection in February 2016.

The nebula Sh2-284 (Image ESO/VPHAS+ team. Acknowledgement: CASU)

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An image captured by the OmegaCAM instrument mounted on ESO’s VST in Chile shows details of the nebula cataloged as Sh2-284. It’s part of the VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+), a survey that included over 500 million objects in the Milky Way to improve our understanding of stars’ life cycles. Sh2-284 is a sort of star nursery whose shape was compared to that of a cat’s face and for this nicknamed “smiling cat”.

The movement of exoplanet AF Lep b, identified in the white spot near the arrows, in images captured in December 2021 and February 2023

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An article published in “Astrophysical Journal Letters” reports the role of the astrometric technique in the discovery of one of the least massive planets so far photographed directly. A team of researchers used the Keck II telescope at the Keck Observatory in Hawaii to photograph the exoplanet cataloged AF Lep b, among the first discovered using the technique of astrometry, which is usually used in conjunction with other astronomical investigation methods. This offers new perspectives in the search for exoplanets.

Artist's concept of the exoplanet TRAPPIST-1 c with its star in the background (Image NASA, ESA, CSA, Joseph Olmsted (STScI). Science: Sebastian Zieba (MPI-A), Laura Kreidberg (MPI-A))

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An article published in the journal “Nature” reports a study on the exoplanet TRAPPIST-1 c which indicates that its atmosphere is very thin or non-existent. A team of researchers used the James Webb space telescope to examine one of the seven planets of the TRAPPIST-1 system and the results allow to rule out the hypothesis that it’s similar to Venus. Thermal emissions indicate a temperature on its surface’s day-side of about 107° Celsius. According to the researchers, this indicates that this exoplanet may have formed with little water.

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An article published in the journal “Nature Astronomy” reports the discovery of a binary system that includes a white dwarf pulsar, the second such object discovered so far. A team of researchers that includes some of those who discovered the first white dwarf pulsar identified J191213.72-441045.1, or simply J1912-4410, a binary system that also includes a normal star belonging to the red dwarf class. This new discovery offers new insight into what constitutes a new class of cosmic objects with the potential to develop models to describe their formation and behavior.