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bystander
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by bystander » Tue May 26, 2020 4:48 pm
Astronomers Discover New Class of Cosmic Explosions
National Radio Astronomy Observatory | 2020 May 26
Astronomers have found two objects that, added to a strange object discovered in 2018, constitute a new class of cosmic explosions. The new type of explosion shares some characteristics with supernova explosions of massive stars and with the explosions that generate gamma-ray bursts (GRBs), but still has distinctive differences from each.
The saga began in June of 2018 when astronomers saw a cosmic blast with surprising characteristics and behavior. The object, dubbed AT2018cow (“The Cow”), drew worldwide attention from scientists and was studied extensively. While it shared some characteristics with supernova explosions, it differed in important aspects, particularly its unusual initial brightness and how rapidly it brightened and faded in just a few days.
In the meantime, two additional blasts — one from 2016 and one from 2018 — also showed unusual characteristics and were being observed and analyzed. The two new explosions are called CSS161010 (short for CRTS CSS161010 J045834-081803), in a galaxy about 500 million light-years from Earth, and ZTF18abvkwla (“The Koala”), in a galaxy about 3.4 billion light-years distant. Both were discovered by automated sky surveys (Catalina Real-time Transient Survey, All-Sky Automated Survey for Supernovae, and Zwicky Transient Facility) using visible-light telescopes to scan large areas of sky nightly.
Two teams of astronomers followed up those discoveries by observing the objects with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA). Both teams also used the Giant Metrewave Radio Telescope in India and the team studying CSS161010 used NASA’s Chandra X-ray Observatory. Both objects gave the observers surprises. ...
In both cases, the follow-up observations indicated that the objects shared features in common with AT2018cow. The scientists concluded that these events, called Fast Blue Optical Transients (FBOTs), represent, along with AT2018cow, a type of stellar explosion significantly different from others. ...
Astrophysicists Capture New Class of Transient Objects
Northwestern University | 2020 May 26
The ‘Cow’ Mystery Strikes Back: Two
More Rare, Explosive Events Captured
W.M. Keck Observatory | 2020 May 26
A Mildly Relativistic Outflow from the Energetic, Fast-rising Blue
Optical Transient CSS161010 in a Dwarf Galaxy ~ D.L. Coppejans
et al
The Koala: A Fast Blue Optical Transient with Luminous Radio
Emission from a Starburst Dwarf Galaxy at z = 0.27 ~ Anna Y. Q. Ho
et al
viewtopic.php?p=301562#p301562
Last edited by
bystander on Tue May 26, 2020 6:25 pm, edited 1 time in total.
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Ann
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Post
by Ann » Tue May 26, 2020 6:39 pm
bystander wrote: ↑Tue May 26, 2020 4:48 pm
Astronomers Discover New Class of Cosmic Explosions
National Radio Astronomy Observatory | 2020 May 26
Astronomers have found two objects that, added to a strange object discovered in 2018, constitute a new class of cosmic explosions. The new type of explosion shares some characteristics with supernova explosions of massive stars and with the explosions that generate gamma-ray bursts (GRBs), but still has distinctive differences from each.
The saga began in June of 2018 when astronomers saw a cosmic blast with surprising characteristics and behavior. The object, dubbed AT2018cow (“The Cow”), drew worldwide attention from scientists and was studied extensively. While it shared some characteristics with supernova explosions, it differed in important aspects, particularly its unusual initial brightness and how rapidly it brightened and faded in just a few days.
In the meantime, two additional blasts — one from 2016 and one from 2018 — also showed unusual characteristics and were being observed and analyzed. The two new explosions are called CSS161010 (short for CRTS CSS161010 J045834-081803), in a galaxy about 500 million light-years from Earth, and ZTF18abvkwla (“The Koala”), in a galaxy about 3.4 billion light-years distant. Both were discovered by automated sky surveys (Catalina Real-time Transient Survey, All-Sky Automated Survey for Supernovae, and Zwicky Transient Facility) using visible-light telescopes to scan large areas of sky nightly.
Two teams of astronomers followed up those discoveries by observing the objects with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA). Both teams also used the Giant Metrewave Radio Telescope in India and the team studying CSS161010 used NASA’s Chandra X-ray Observatory. Both objects gave the observers surprises. ...
In both cases, the follow-up observations indicated that the objects shared features in common with AT2018cow. The scientists concluded that these events, called Fast Blue Optical Transients (FBOTs), represent, along with AT2018cow, a type of stellar explosion significantly different from others. ...
Astrophysicists Capture New Class of Transient Objects
Northwestern University | 2020 May 26
A Mildly Relativistic Outflow from the Energetic, Fast-rising Blue Optical Transient CSS161010 in a Dwarf Galaxy ~ D.L. Coppejans
et al
The Koala: A Fast Blue Optical Transient with Luminous Radio
Emission from a Starburst Dwarf Galaxy at z = 0.27 ~ Anna Y. Q. Ho
et al
viewtopic.php?p=301562#p301562
I was, of course, extremely interested in why this kind of explosion was called "blue" (or rather, why it was called a Fast Blue Optical Transient). Never mind, in what way was this fast optical transient "blue"?
Wikipedia provided some of the answers as to why AT2018cow (“The Cow”) would be called blue.
Wikipedia wrote:
The first X-ray and ultraviolet (UV) observations of AT 2018cow were obtained on 19 June 2018 with the Swift telescope.[25] These observations revealed that the object was a bright X-ray/UV transient, with an X-ray luminosity of ~1×1043 erg/s and a
UV brightness of about 11.7 (Vega mag) in the range 1600-3600 Å.
...
According to astronomers at the time of its discovery, the explosion, with a surface temperature of over 8,900 °C (16,000 °F;
9,200 K) and traveling 20,000 km/s (12,000 mi/s),[16] may have been a cataclysmic variable star (CV), gamma-ray burst (GRB), gravitational wave (GW), supernova (SN), or something else.
9,200 K is very similar to the temperature of Vega:
Jim Kaler wrote:
Vega is a classic class A (A0) white main sequence dwarf star, like the Sun quietly running off the nuclear fusion of hydrogen deep in its core, with a sort of average effective surface temperature of about 9500 degrees Kelvin.
Of course, Jim Kaler was wrong in stating that Vega is white! Vega is a visibly blue star. Its color is obvious when seen through a telescope.
So AT2018cow (“The Cow”) was a Cow of an explosion the color of Vega!
Ann
Color Commentator
