THE MOST!
Most proper motion of ejecta launched from a massive radio source binary, x-ray binary, 'black hole' binary system, it's MAXI J1348–630! A dubious distinction, but a distinction nonetheless!
MARCH 30, 2021 REPORT
Astronomers inspect black hole X-ray binary MAXI J1348–630
An international team of astronomers has carried out a comprehensive radio and X-ray monitoring of a black hole X-ray binary known as MAXI J1348–630. The observational campaign provided important insights into the evolution of the source's compact and transient jets. The study was presented in a paper published March 22 on arXiv.org.
Black hole X-ray binaries (BHXBs) are binary systems consisting of a black hole orbited by a stellar companion, typically a low-mass, evolved star. In BHXBs, X-rays are produced by material accreting from a secondary companion star onto a black hole primary. Such systems are usually detected in outbursts when the X-ray flux increases significantly.
MAXI J1348–630 was initially detected on January 26, 2019 as a bright X-ray transient by the Monitor of All-sky X-ray Image (MAXI) aboard the International Space Station (ISS). Further observations of this source confirmed that it is a BHXB with a black hole mass of about seven solar masses at a distance of some 7,170 light years away from the Earth.
Almost immediately after the bursting activity of MAXI J1348–630 started, a group of astronomers led by Francesco Carotenuto of the University of Paris, France, commenced a monitoring campaign of this source with the aim of shedding more light on its nature. They observed MAXI J1348–630 in the radio band with the MeerKAT telescope in south Africa and the Australia Telescope Compact Array (ATCA), and also in the X-rays using MAXI and NASA's Swift spacecraft.
"In this work, we have presented the X-ray and radio monitoring of MAXI J1348–630 during its 2019/2020, discovery outburst. With our X-ray monitoring, we have been able to follow the whole outburst," the researchers wrote in the paper.
The observations show that during the outburst MAXI J1348–630 exhibited a rather typical X-ray evolution in the first part, completing a whole cycle in the hardness-density diagram (HID), and then showcased a complex sequence of hard-state-only re-brightenings in the second part.
During the outburst, Carotenuto's team observed the rise, quenching, and re-activation of the compact jets. They also identified two single-sided discrete ejecta, launched about two months apart and traveling away from the black hole. These ejecta had proper motion at a level of some 100 mas/day—the highest proper motion measured so far for such features in BHXBs.
The astronomers found that the first ejection happened during the hard-to-soft state transition of the source, before a strong radio flare. When it comes to the second ejection, it was launched during a short excursion from the soft to the intermediate state.
According to the authors of the paper, the results suggest that MAXI J1348–630 appears to be inside a low-density cavity in the interstellar medium (ISM).
"After traveling with constant speed, the first component underwent a strong deceleration, which was covered with unprecedented detail and suggested that MAXI J1348–630 could be located inside a low-density cavity in the interstellar medium, as already proposed for XTE J1550–564 and H1743–322," the researchers concluded.
source: phys.org
SMALLEST WHITE DWARF- smaller than the Moon and more massive than... the Sun?
A white dwarf living on the edge
Astronomers have discovered a stellar corpse known as a white dwarf that is roughly the size of Earth's moon. The white dwarf is about 4,300 kilometers across, while the moon is 3,500 kilometers across. The white dwarf is depicted above the moon in this artistic representation; in reality, the white dwarf lies 130 light-years away in the constellation of Aquila. Credit: Giuseppe Parisi
Astronomers have discovered the smallest and most massive white dwarf ever seen. The smoldering cinder, which formed when two less massive white dwarfs merged, is heavy, "packing a mass greater than that of our Sun into a body about the size of our Moon," says Ilaria Caiazzo, the Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Astrophysics at Caltech and lead author of the new study appearing in the July 1 issue of the journal Nature. "It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead regulated by quantum mechanics."
The discovery was made by the Zwicky Transient Facility, or ZTF, which operates at Caltech's Palomar Observatory; two Hawai'i telescopes—W. M. Keck Observatory on Maunakea, Hawai'i Island and University of Hawai'i Institute for Astronomy's Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui—helped characterize the dead star, along with the 200-inch Hale Telescope at Palomar, the European Gaia space observatory, and NASA's Neil Gehrels Swift Observatory.
White dwarfs are the collapsed remnants of stars that were once about eight times the mass of our Sun or lighter. Our Sun, for example, after it first puffs up into a red giant in about 5 billion years, will ultimately slough off its outer layers and shrink down into a compact white dwarf. About 97 percent of all stars become white dwarfs.
While our Sun is alone in space without a stellar partner, many stars orbit around each other in pairs. The stars grow old together, and if they are both less than eight solar-masses, they will both evolve into white dwarfs.
The new discovery provides an example of what can happen after this phase. The pair of white dwarfs, which spiral around each other, lose energy in the form of gravitational waves and ultimately merge. If the dead stars are massive enough, they explode in what is called a type Ia supernova. But if they are below a certain mass threshold, they combine together into a new white dwarf that is heavier than either progenitor star. This process of merging boosts the magnetic field of that star and speeds up its rotation compared to that of the progenitors.
Astronomers say that the newfound tiny white dwarf, named ZTF J1901+1458, took the latter route of evolution; its progenitors merged and produced a white dwarf 1.35 times the mass of our Sun. The white dwarf has an extreme magnetic field almost 1 billion times stronger than our Sun's and whips around on its axis at a frenzied pace of one revolution every seven minutes (the zippiest white dwarf known, called EPIC 228939929, rotates every 5.3 minutes).
"We caught this very interesting object that wasn't quite massive enough to explode," says Caiazzo. "We are truly probing how massive a white dwarf can be."
What's more, Caiazzo and her collaborators think that the merged white dwarf may be massive enough to evolve into a neutron-rich dead star, or neutron star, which typically forms when a star much more massive than our Sun explodes in a supernova.
This illustration highlights a newfound small white dwarf, discovered by ZTF, that is 4,300 kilometers across, or roughly the size of Earth's moon, which is 3,500 kilometers across. The two bodies are shown next to each other for size comparison. The hot, young white dwarf is also the most massive white dwarf known, weighing 1.35 times as much as our sun. Credit: Giuseppe Parisi
"This is highly speculative, but it's possible that the white dwarf is massive enough to further collapse into a neutron star," says Caiazzo. "It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed."
If this neutron star formation hypothesis is correct, it may mean that a significant portion of other neutron stars take shape in this way. The newfound object's close proximity (about 130 light-years away) and its young age (about 100 million years old or less) indicate that similar objects may occur more commonly in our galaxy.
Magnetic and fast
The white dwarf was first spotted by Caiazzo's colleague Kevin Burdge, a postdoctoral scholar at Caltech, after searching through all-sky images captured by ZTF. This particular white dwarf, when analyzed in combination with data from Gaia, stood out for being very massive and having a rapid rotation.
"No one has systematically been able to explore short-timescale astronomical phenomena on this kind of scale until now. The results of these efforts are stunning," says Burdge, who, in 2019, led the team that discovered a pair of white dwarfs zipping around each other every seven minutes.
The team then analyzed the spectrum of the star using Keck Observatory's Low Resolution Imaging Spectrometer (LRIS), and that is when Caiazzo was struck by the signatures of a very powerful magnetic field and realized that she and her team had found something "very special," as she says. The strength of the magnetic field together with the seven-minute rotational speed of the object indicated that it was the result of two smaller white dwarfs coalescing into one.
Data from Swift, which observes ultraviolet light, helped nail down the size and mass of the white dwarf. With a diameter of 2,670 miles, ZTF J1901+1458 secures the title for the smallest known white dwarf, edging out previous record holders, RE J0317-853 and WD 1832+089, which each have diameters of about 3,100 miles.
In the future, Caiazzo hopes to use ZTF to find more white dwarfs like this one, and, in general, to study the population as a whole. "There are so many questions to address, such as what is the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type Ia supernovae? How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs? Finding a large population of white dwarfs born from mergers will help us answer all these questions and more."
More information: Caiazzo, I. et al, A highly magnetized and rapidly rotating white dwarf as small as the Moon, Nature (2021). DOI: 10.1038/s41586-021-03615-y
Journal information: Nature
Provided by W. M. Keck Observatory
Geminga Pulsar
THE MOST BRIGHT GAMMA RAY SOURCE?
Credit: ESA/Dr. P. Caraveo
Geminga's Trick of the Tail
Gamma ray sources are among the most mysterious objects in the sky. This is partly due to the high-energy nature of gamma rays, which require inherently extreme conditions to be produced. This is also partly due to the difficulty in imaging gamma rays, and the inherently poor spatial resolution of early gamma ray detectors, which made it difficult to associate gamma ray sources with objects seen in other wavelengths. One of the most mysterious was Geminga, a bright pulsing source of gamma rays in the constellation of Gemini, discovered in the 1970's but not identified until about 20 years later. Astronomers now know Geminga is a pulsing X-ray source and, at about 500 light-years, one of the nearest neutron stars known. It is also a rare example of a class of "radio quiet" neutron stars and as such a item of intense interest to astronomers. A new observation of Geminga by the EPIC camera on the XMM-Newton X-ray Observatory reveals another of Geminga's tricks: as the neutron star plows through space nearly perpendicular to our line of sight (at about 270 thousand miles per hour) it creates a bow shock. The edge of this shock appears as two "tails" visible in the image above.
(Source https://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/compact_objects/geminga_tails_xmm.html )
Wow Dan you shine .The exposure you have to cosmology is due only to a real love of this science..What is with the Fast radio bursts? Gam,ma / radio bursts are not sorces.. are not the same. I dont understand what one arc min means to my eve . It is moving very fast / how big is it?isit known? If we can see the tails its volisity ( direction?) Speed .Does that mean it is moving in front of us. The enery is really out of this world. Would really love to get a hiogh res image. Thanks.
