NGC 3079
Credit X-ray: NASA/CXC/University of Michigan/J-T Li et al.; Optical: NASA/STScI
We all know bubbles from soapy baths or sodas. These bubbles of
everyday experience on Earth are up to a few inches across, and consist
of a thin film of liquid enclosing a small volume of air or other gas.
In space, however, there are very different bubbles — composed of a
lighter gas inside a heavier one — and they can be huge.
The galaxy NGC 3079, located about 67 million light years
from Earth, contains two "superbubbles" unlike anything here on our
planet. A pair of balloon-like regions stretch out on opposite sides of
the center of the galaxy: one is 4,900 light years across and the other
is only slightly smaller, with a diameter of about 3,600 light years.
For context, one light year is about 6 trillion miles, or 9 trillion
kilometers.
The superbubbles in NGC 3079 give off light in the form of X-ray, optical and radio emission, making them detectable by NASA telescopes. In this composite image, X-ray data from NASA's Chandra X-ray Observatory
are shown in purple and optical data from NASA's Hubble Space Telescope
are shown in orange and blue. A labeled version of the X-ray image
shows that the upper superbubble is clearly visible, along with hints of
fainter emission from the lower superbubble.
NGC 3079 (Labeled)
Credit: NASA/CXC/University of Michigan/J-T Li et al.
New observations from Chandra show that in NGC 3079 a cosmic particle
accelerator is producing ultra-energetic particles in the rims of the
superbubbles. These particles can be much more energetic than those
created by Europe's Large Hadron Collider (LHC), the world's most
powerful human-made particle accelerator.
The superbubbles in NGC 3079 provide evidence that they and
structures like them may be the source of high-energy particles called "cosmic rays" that regularly bombard the Earth. Shock waves
— akin to sonic booms caused by supersonic planes — associated with
exploding stars can accelerate particles up to energies about 100 times
larger than those generated in the LHC, but astronomers are uncertain
about where even more energetic cosmic rays come from. This new result
suggests superbubbles may be one source of these ultra-energetic cosmic
rays.
The outer regions of the bubbles generate shock waves as they expand
and collide with surrounding gas. Scientists think charged particles
scatter or bounce off tangled magnetic fields
in these shock waves, much like balls rebounding off bumpers in a
pinball machine. When the particles cross the shock front they are
accelerated, as if they received a kick from a pinball machine's
flipper. These energetic particles can escape and some may eventually
strike the Earth's atmosphere in the form of cosmic rays.
The amount of radio waves or X-rays at different wavelengths, or
"spectra," of one of the bubbles suggest that the source of the emission
is electrons
spiraling around magnetic field lines, and radiating by a process
called synchrotron radiation. This is the first direct evidence of synchrotron radiation
in high energy X-rays from a galaxy-sized superbubble, and it tells
scientists about the maximum energies that the electrons have attained.
It is not understood why synchrotron emission is detected from only one
of the bubbles.
The radio and X-ray spectra, along with the location of the X-ray
emission along the rims of the bubbles, imply that the particles
responsible for the X-ray emission must have been accelerated in the
shock waves there, because they would have lost too much energy while
being transported from the center of the galaxy.
NGC 3079's superbubbles are younger cousins of "Fermi bubbles," first
located in the Milky Way galaxy in 2010. Astronomers think such
superbubbles may form when processes associated with matter falling into
a supermassive black hole
in the center of galaxy, which leads to the release of enormous amounts
of energy in the form of particles and magnetic fields. Superbubbles
may also be sculpted by winds flowing from a large number of young,
massive stars.
A paper describing these results was led by Jiangtao Li of the
University of Michigan and appears in The Astrophysical Journal. It is
also available online.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts,
controls Chandra's science and flight operations.
Fast Facts for NGC 3079:
Scale: Image is 3.2 arcmin (about 62,000 light years) across.
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000) : RA 10h 01m 57.8s | Dec +55° 40´ 47.2"
Constellation: Ursa Major
Observation Date: 4 observations: Mar 7, 2001; Dec 27, 2006; Jan 30, 2018; Feb 1, 2018
Observation Time: 35 hours 45 min (1 day 11 hours 45 minutes)
Obs. ID: 2038, 7851, 19307, 20947
Instrument: ACIS
References: Li, J-T. et al, 2019, ApJ, accepted. arXiv:1901.10536
Color Code X-ray: purple & pink; Optical: red & blue
Distance Estimate: About 67 million light years
Source: NASA’s Chandra X-ray Observatory
