Astronomers discovered a huge black arc in the constellation URSA major

In the constellation URSA major
discovered a narrow, but long region of ultraviolet radiation. It stretches
thirty degrees is about the length of the asterism of the Big Dipper from the end of the “handle” to the outer edge of the “bucket”. Unusual arc may have formed
as a result of shock events in the interstellar medium in the Solar vicinity
the system writes the group
astronomers in the paper on arXiv.org. Article accepted for publication in Astronomy & Astrophysics.

The space between the stars in
the galaxy, which is called the interstellar medium filled with gas and dust,
however, the density of this medium is extremely low. Recently, the interest
researchers are attracted to the linear structure in the interstellar medium, which are detected
when observed in different bands on the radio frequency of neutral hydrogen emission
dust, low-frequency polarized radio emission. It is believed that the study
these structures can affect our ideas about the Solar vicinity
system and the galaxy as a whole.

In 2001, American
astronomers Peter Makalat (Peter McCullough) and Robert Benjamin (Robert Benjamin) said
about the discovery in the constellation the Big dipper is unusually straight and thin
ionized structures visible in H-alpha and is similar to the thread. It could be
their assumptions, jet, low-density filament nebula, a trail of ionisation,
left compact source (e.g. a neutron star), or trail
ionized gas left by a source of low luminosity. Astronomers
leaning towards the last option — so-called relic trail Stromgren — despite the fact that there is no logical explaining a trace of the body was never found.

In the new work, a team of astronomers from France,
The Netherlands and the USA under the leadership of Andrea Bracco (Bracco Andrea) of
Croatian Institute of Rugera of Bošković investigated the open at the beginning of the XXI century structure
in different wavelengths and found that it is also visible in the far
ultraviolet (wavelength 130-180 nm) and near ultraviolet (170-280
nanometers) on the images from the space telescope GALEX (Galaxy Evolution Explorer). These
the images cover a much larger area of the sky than the pictures taken
Makalapa and Benjamin in H-alpha. They can be clearly seen that line,
discovered by American scientists in 2001, is a fragment of a much
larger structures, reminiscent of the arc, and it consists of multiple small arches.

If the hypothesis that
suggested Makalat and Benjamin, was correct, their thread would be straight. But the Bracco group found that the arches are not aligned in a single straight line. In addition, image search
the nearest white dwarfs and hot subcortical in the far ultraviolet
when compared with their parallaxes and movement of received space
apparatus Gaia, gave no results
which would correspond to found in 2001 by thread. So the hypothesis of a relict track Stromgren had to be abandoned.

Astronomers have discovered that most of the smaller arches lie
along approximately one-sixth of a circle with an angular radius of about 29 degrees. This
a circle with an area of 2681 square degree is 6.5 percent of the area of the entire sky. Region
inside the circle the Big dipper is well-known as the region with the lowest
the density of neutral hydrogen in the line of sight that includes the famous
Hole of Lokman, which is near the asterism of the Big Dipper. This area seems attractive for interstellar research, however, you must carefully study the properties of the medium in it, not to ascribe intergalactic objects properties, which are actually caused by features of the interstellar medium in this region.

Bracco and colleagues believe that the arc of the Big dipper was formed
the explosion of a supernova, which occurred, presumably, in
few hundred parsecs from the Solar system. The fact that we observed lines of ions, not neutral atoms, indicates hot
gas with a temperature of more than 10000 Kelvin, which is typical for areas of impact
events in the interstellar medium. Also, the recombination of gas, experienced a shock wave,
leads to two-photon emission in the ultraviolet range. Radial shock
the waves are likely the primary mechanism of dissipating the kinetic
energy waves that arise as a result of the supernova explosion.

To test this idea, studies were conducted
the images in the far ultraviolet four circular formations with a diameter of more
10 degrees. All selected for comparison of the objects contained thin structures, resembling
arches in the arc of the Big dipper, but much smaller. The thinness and fragmentation of the arc into separate arch caused by, apparently, the fact that we are looking at the edge is not perfect, and slightly “creased” areas, like painting, which is observed in the remnants of the supernova explosion of the Cygnus Loop. Further
research open arc astronomers will help better understand its physical
the parameters and more accurately measure the distance to it.

Studying supernovae is a very promising direction
in modern astrophysics. We described how scientists have made imaging of young supernovae in the Large Magellanic
the cloud, and how relatively “fresh” ashes of a supernova discovered in Antarctica. And
here you can view
three-dimensional visualization of the explosion of such stars.

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