- 3898 - RADIO WAVES - are “light” for new telescopes. Astronomers capture a radio signal from ancient galaxy at a record-breaking distance. The signal was detected at a special and significant wavelength known as the "21-centimeter line" or the "hydrogen line," which is emitted by neutral hydrogen atoms.
-------------- 3898 - RADIO WAVES - are “light” for new telescopes.
- The radio
signal from the star-forming galaxy
”SDSSJ0826+5630” was emitted when our 13.8 billion-year-old galaxy was
just 4.9 billion years old. The signal allowed the astronomers to measure the
galaxy's gas content and find that its mass is double that of the early
galaxy's visible stars.
-
- Galaxies
emit electromagnetic radiation, or light, across a wide range of radio
wavelengths, but 21-cm-wavelength radio waves have only been seen from nearby
and thus more recent galactic sources.
-
- This is the
equivalent to a look-back in time of 8.8 billion years. As the Universe expands the light waves get
stretched out to where we see them as radio waves. The difficulty in spotting these wavelengths
from more distant galaxies is due to the fact that as electromagnetic radiation
from early galaxies travels vast distances to Earth, the expansion of the
universe stretches its wavelength and causes its energy to reduce.
-
- That means
telescopes here on Earth need a natural boost to see long-wavelength,
low-energy radio waves like the hydrogen line signal.
-
- General
relativity suggests that objects with mass warp spacetime similar to how a ball
placed on a stretched rubber sheet would weigh it down in the center, and just
like in that analogy, the greater the mass, the more extreme the curvature.
-
- That means
a tremendously massive object like a black hole or galaxy causes extreme
curvature in spacetime just as a bowling ball would cause the extreme curvature
of the rubber sheet in the analogy.
-
- This
curving of spacetime causes light to bend as well as it passes by objects of
tremendous mass. A phenomenon known as “gravitational lensing” occurs when a
foreground or lensing object of tremendous mass sits between an observer and a
background source, causing the light from the background object to curve and take
different paths through and around the lensing object. This can not only make a
single object appear at multiple points in the sky, but it can also have the
effect of magnifying this light.
-
- This could
open up a new way of using “long-wavelength radio telescopes” to probe the
evolution of stars and galaxies and how the early universe evolved into the
cosmos we see around us in its current era.
-
- In 1979,
astronomers spotted two nearly identical quasars that seemed close to each
other in the sky. These so-called “Twin Quasars” are actually separate images
of the same object. The light paths
that created each image traveled through different parts of the cluster.
-
- One path
took a little longer than the other. That meant a flicker in one image of the
quasar occurred 14 months later in the other. The reason? The cluster’s mass
distribution formed a lens that distorted the light and drastically affected
the two paths.
-
- In
2022, astronomers reported a similar
effect with another distant quasar. They spent fourteen years measuring an even
longer time delay between multiple images of this target quasar.
-
- The combo of
galaxies and dark matter in the cluster is really entangling the quasar light
as it passes through. That’s causing the light to travel different trajectories
through the gravitational lens. The result is the same strange time-delayed
effect.
-
- The four
images of the quasar that we observe actually correspond to a single quasar
whose light is curved on its path towards us by the gravitational field of the
galaxy cluster. Since the trajectory
followed by the light rays to form each image is different, we observe them at
different instants of time. We have to
wait 6.73 years for the signal we observed in the first image to be reproduced
in the fourth one.
-
- The Sloan
Digital Sky Survey first discovered cluster “SDSS J1004+4112”. Hubble Space
Telescope imaged it in 2006. It was the first image of a single quasar with its
light split into five images by lensing.
-
- Galaxy
clusters are astonishingly massive and the largest gravitationally bound
structures we know of in the universe. Some contain thousands of galaxies. The
combined gravity of the galaxies, plus the intermingled dark matter in the
cluster can entangle light from more distant objects as it passes through or
near the cluster. It turns out that the mass of all the “stuff” in the cluster
is spread out unevenly. That can affect the path of light through the cluster.
-
- Measuring
these time delays helps to better understand the properties of galaxies and
clusters of galaxies, their mass, and its distribution, in addition to
providing new data for the estimation of the Hubble constant for the expansion
rate for the Universe. New light curves
for the four bright images occurred over 14.5 years at the 1.2-meter telescope.
-
- A glowing
blob known as "the cocoon," which appears to be inside one of the
enormous gamma-ray emanations from the center of our galaxy dubbed the
"Fermi bubbles," has puzzled astronomers since it was discovered in
2012.
-
- The
“cocoon” is caused by gamma rays emitted by fast-spinning extreme stars called
"millisecond pulsars" located in the Sagittarius dwarf galaxy, which
orbits the Milky Way. Thankfully for
life on Earth, our atmosphere blocks gamma rays. These are particles of light
with energies more than a million times higher than the photons we detect with
our eyes.
-
- Because our
ground-level view is obscured, scientists had no idea of the richness of the
gamma-ray sky until instruments were lofted into space. But, starting with the
discoveries made by the Vela satellites put into orbit in the 1960s to monitor
the Nuclear Test Ban, more and more of this richness has been revealed.
-
- The state-of-the-art
gamma-ray instrument operating today is the “Fermi Gamma Ray Space Telescope',
a large NASA mission in orbit for more than a decade. Fermi's ability to
resolve fine detail and detect faint sources has uncovered a number of
surprises about our Milky Way and the wider universe.
-
- One of
these surprises emerged in 2010,
something in the Milky Way's center is blowing what look like a pair of
giant, gamma-ray-emitting bubbles. These completely unanticipated "Fermi
bubbles" cover fully 10% of the sky.
-
- A prime
suspect for the source of the bubbles is the galaxy's resident supermassive
black hole. This black hole, 4 million times more massive than the Sun, lurks
in the galactic nucleus, the region from which the bubbles emanate.
-
- Most
galaxies host such giant black holes in their centers. In some, these black
holes are actively gulping down matter. Thus fed, they simultaneously spew out
giant, outflowing "jets" visible across the electromagnetic spectrum.
-
-
Astronomers found this structure has nothing to do with the Fermi
bubbles or, indeed, the galaxy's supermassive black hole. Rather, they found the cocoon is actually
something else entirely: gamma rays from the Sagittarius dwarf galaxy, which
happens to be behind the southern bubble as seen from the position of Earth.
-
- The
Sagittarius dwarf, so called because its sky position is in the constellation
of Sagittarius, is a "satellite" galaxy orbiting the Milky Way. It is
the remnant of a much larger galaxy that the Milky Way's strong gravitational
field has literally ripped apart. Stars
pulled out of the Sagittarius dwarf can be found in "tails" that wrap
around the entire sky.
-
- In the Milky
Way, the main source of gamma rays is when high-energy particles, cosmic rays,
collide with the very tenuous gas between the stars. However, this process cannot explain the
gamma rays emitted from the Sagittarius dwarf. It long ago lost its gas to the
same gravity that pulled away so many of its stars.
-
- So where do
the gamma rays come from? What type of
source amongst such a population produces gamma rays? Rapidly spinning objects called
"millisecond pulsars." are the
remnants of particular stars, significantly more massive than the sun, are
closely orbiting another star.
-
- Under just
the right circumstances, such binary systems produce a “neutron star”, an
object about as heavy as the sun but only about 20 km across, that rotates
hundreds of times per second.
-
- Because of
their rapid rotation and strong magnetic field, these neutron stars act as
natural particle accelerators: they launch particles at extremely high energy
into space. These particles then emit
gamma rays. Millisecond pulsars in the Sagittarius dwarf were the ultimate
source of the mysterious cocoon.
-
- These
findings shed new light on millisecond pulsars as sources of gamma rays in
other old stellar systems. The hunt for
dark matter signals goes on.
-
March 1, 2023 RADIO WAVES - are
“light” for new telescopes
3898
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--- Friday, March 3, 2023
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