The high-energy universe - The Universe in my pocket - Mimoza Hafizi Tirana University
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
The Universe in my pocket
The high-energy universe
Mimoza Hafizi
No. 9
ES-001 Tirana University
Even with the naked eye, we can
see that some celestial objects
are brighter than others. Are they
closer to us and thus look brighter?
Or do they release more energy?
Astronomers know how to measure
the distances of many celestial
bodies, so they can estimate the
energy these emit in visible light.
In the Cassiopeia Constellation, the five Using special detectors working in
brightest stars form a ‘W’ shape. These the high-energy domain they can also
stars are up to a thousand times more
powerful than our Sun. But they do not
gauge the energy that is invisible to the
emit in the high-energy domain. eye, being emitted by high-energy
Special instruments used for high-energy photons (UV, X and gamma-rays*),
astrophysics are able to detect UV, X high-energy particles (neutrinos,
and gamma rays released by certain cosmic rays) and gravitational waves.
objects. Photometers measure the Some of the objects emitting in the
amount of light coming from these high-energy domain, like Supernovae,
objects and provide us with an accurate
measurement of the total energy they
Neutron Stars, Black Holes or
release. Active Galactic Nuclei emit extreme
Many objects emitting at high energies amounts of energy. They radiate billions
cannot be detected in visible light. of times more energy than our Sun.
2 *see TUIMP 2 3
Left: In the star Supernovae
map of
Cassiopeia, the What a surprise if you watch the sky
astronomer and suddenly observe a new star
Tycho Brahe shining in a place that was empty
marked by ‘I’ the before! Maybe you would cry: A new
‘new-born star’, star is born! A nova, in Latin. Or, a
on 11 November supernova, if the new light is extremely
1572, later powerful! The first such case was
named Tycho’s
When it appeared, that of the guest-star seen by
supernova. ‘F’,
Tycho’s supernova was ‘E’, ‘D’, ‘C’, ‘B’, ‘A’, Chinese Astronomers in 1054*.
as bright as Venus, ‘G’ are long- In fact this light does not signal the
although the burst lasting stars, birth of a new star: A supernova is
occurred about 9 light- and can be seen the explosion of an existing star.
years away. It dimmed in the photo of
The burst is so tremendous that in
day after day and after Cassiopeia on
about two years it
a few minutes it releases as much
page 2, but the
could no longer be seen ‘I’ star is no energy as our Sun during its
with the naked eye. longer seen.
lifetime of10 billion years!
Afterwards, the burst decays and
Left: The supernova
2010ltd, discovered by a
the star becomes invisible again.
ten-year old girl, Kathryn What remains is a neutron star or
Gray. The burst happened a black hole. Telescopes show a large
240million light-years away. amount of matter moving away.
*see TUIMP 10 5
4Black holes
When a star with mass above 30
solar masses explodes as a
supernova, a black hole of several
solar masses forms in its center,
Left: A diagram demonstrating the inside a region of a few kilometers.
collision between two black holes. The
ripples propagating like waves in a pool Why this unusual name? Because a
represent gravitational waves. black hole has such strong gravity
The first gravitational wave detected by that nothing can escape from it.
humans on 14 September 2015 No light, nor particles!
informed us about such a collision, that
How then, can we observe them? By
happened 1.3 billion years ago between a
pair of black holes of 36 and 29 solar their influence on their surroundings!
masses. The power released during such a Their gravitational energy is huge,
collision reached a level greater than that because their mass is concentrated
of the light radiated by all the stars in in a very small region. This energy
the Universe! can be released in the form of
Right: A photo of the LIGO Hanford site, gravitational waves.
one of the observatories where Gravitational waves were observed
gravitational waves are detected. The
for the first time in September
observed waveform matches the
predictions of General Relativity
2015. They were radiated by the
developed by Albert Einstein. collision of two black holes.
6 7Neutrinos Neutron stars
Neutrinos are elementary particles When a star with mass between 8
with no charge and with a tiny, as yet and 30 solar masses explodes as
undetermined, mass. They interact a supernova, a neutron star forms.
very weakly with other matter, so it is It is so dense that one teaspoonful
hard to detect them. Some giant would weigh a billion tons!
experiments have been established Neutron stars are composed of
on Earth to detect neutrinos. neutrons and rotate up to several
Neutrinos are created by nuclear hundred times per second,
reactions, such as those taking accelerating the particles in their
place in the core of a star or in atmosphere to near-light speed and
nuclear experiments. In supernova generating a narrow radiating beam.
explosions, more than 99% of the In some cases, this beam sweeps
energy can be released as neutrinos. across the Earth, making these
Despite their small mass, neutrinos are stars detectable as pulsars*. The
thought to be so numerous that they can fastest pulsar, PSR J1748-2446ad,
influence the history of the Universe. rotates 716 times per second!
Right : The IceCube Neutrino During the supernova burst leading to
Observatory. Thousands of neutron star formation, apart from
sensors are placed under light, a huge stream of neutrinos leaves
the Antarctic ice, distributed the star at nearly the speed of light.
over a cubic kilometer for Some of these are observed on Earth.
detecting neutrinos.
8 * See TUIMP 10 9Left: The Fermi Gamma- Gamma Ray Bursts
ray Space Telescope,
which detects gamma- Gamma Ray Bursts (GRB) are the
rays, the most energetic most powerful electromagnetic
form of radiation, a million events known to happen in the
times more energetic than visible light. Universe. Their energy, mostly
On 17 August 2017, the Fermi
released in the form of gamma
telescope detected a short Gamma Ray photons*, can exceed one thousand
Burst (GRB), just 1.7 seconds after a times that of a supernova.
gravitational wave signal had reached Discovered fifty years ago, their
Earth observatories. Both of these physics is not yet fully understood.
signals originated from the same event,
two merging neutron stars, 130 million GRB can be of short duration (from
light-years away. Later, this event was tens of milliseconds to few
observed in X-rays, ultraviolet light, and seconds) or long duration (from
other bands of the electromagnetic seconds up to hours). Long GRBs
spectrum. are linked with the burst of a star,
during a supernova explosion. Short
Right: The same GRB GRBs are thought to originate from
seen in X-rays by the the merging of two neutron stars or
Chandra Space of a neutron star and a black hole.
observatory, 9 days Satellite telescopes discover about
after the burst.
one GRB per day.
*see TUIMP 2
10 11Cosmic rays
Not only photons, neutrinos and
gravitational waves reach us from
Space. The high-energy Universe
also sends us charged particles,
mostly protons, but also electrons
and nuclei of atoms; these are
called cosmic rays. Billions of
An artist’s view of the impact of cosmic
rays with the Earth’s atmosphere. Upon
billions of cosmic ray particles
interaction with the atmospheric bombard Earth from Space every
molecules, a ‘shower’ of elementary second.
particles is produced. Some of these Discovered at the beginning of the
particles may reach some of the
20th century, they are still of
thousands of detectors deployed by
scientists in grids covering several uncertain origin.
thousand square kilometers. Cosmic ray particles can carry huge
After a century of numerous energies, and travel nearly at the
experiments, the scientific data up to speed of light. In extreme cases,
now lead to the conclusion that a their kinetic energy can be billions of
significant fraction of cosmic rays
billions of times greater than their
originate from outside our Galaxy, in
supernova explosions or from Active rest-mass energy.
Galactic Nuclei*.
*see TUIMP 6 12 13An illustration
demonstrating
the collision
The five brightest between two
stars of the Cassiopea black holes
constellation are
1000 times more
powerful than our Sun.
Quiz But this is not what is
called high energy!
Which of these GW170817
images is not event seen by
Chandra
related to high
Space
energy phenomena observatory
The supernova
of the Universe? in X rays.
2010ltd.
The impact of
cosmic rays with
Answers on overleaf the Earth’s
atmosphereThe Universe in my pocket No. 9
This booklet was written in 2018 by
Mimoza Hafizi from Tirana University
(Albania)
Nr 1 and revised by Stan Kurtz from the
UNAM Radio Astronomy Institute in Morelia
(Mexico).
Cover image: Artist’s illustration of two
merging neutron stars. [Credit: NSF/
LIGO/Sonoma State University/A.
Simonnet]
To learn more about this
series and about the topics
presented in this booklet,
please visit
http://www.tuimp.org
TUIMP Creative CommonsYou can also read
