Download Gravitational Waves

Gravitational Waves
Angelina Dirina
Astronomy 101
Spring 2016
Gravitational Waves
• Waves that travel at the speed of light and transmit
distortions of space through the universe.
• These are caused by sudden changes of curvature of
spacetime, and move outward through the universe like
ripples in a pond.
• While highly plausible through Einstein’s theories of
relativity, no waves were proven or detected until very
recently.
Theories of Relativity
• Gravitational waves were predicted by Einstein’s theories
of relativity.
• Special relativity (1905) states that space and time are
intertwined, but does not address gravity.
• General relativity (1915) presents gravity into interactions
between space and time. Based on this theory, gravity can
distort and change interactions of space and time.
Spacetime & Curvature
• In order to understand gravitational waves, we must remember
that spacetime deals with four dimensions of possible motion:
length, width, depth, and time.
• Within these four dimensions, gravity allows for the curvature of
spacetime.
• According to Einstein, objects with large gravitational force create
that curvature, such as the Earth going around the Sun – this
proves that spacetime is curved around the Sun.
Ways to Manipulate Curvature
•
Greater curvature of spacetime =
stronger gravity
•
1 way: increase the mass of an object,
and you will have greater
gravitational attraction, hence more
curvature in spacetime
•
Another way: increase the density of
an object’s mass by making it smaller,
like a star that becomes compressed
into a black hole.
•
Black holes have very strong
gravitational attraction, so strong that
nothing that comes near them can
escape.
Source: APA
Discovery!
• In September 2015, the
gravitational-wave detector
detected a small ripple in spacetime
• This ripple was caused by the
merging of two black holes colliding
a billion light years away
• Their gravitational energy combined
was so powerful that this ripple
traveled through the universe, and
eventually made it through Earth
Source: LIGO
Discovery!
• Finally, Einstein’s theories on
gravitational energy were
proven true, indicating that
gravity can produce curvatures
in spacetime that expand and
travel great distances
• These waves traveled at the
the speed of light and
compressed spacetime as they
traveled, which is how LIGO
was able to detect them
Source: Forbes
New Ways to Look at the Universe
• The waves detected by LIGO in September
are only one kind of gravitational energy
people can learn about in the future
• With these new understandings, we can
develop a better knowledge of how the
universe works
New Ways to Look at the Universe
• With these discoveries, we can now observe and study:
– Compact, fast-moving objects: like the wave already detected
by LIGO
– Slower, or more massive objects: all sorts of objects emit
gravity in space, but many of them do not have very strong
gravitational energy, so their signals are harder to detect. A
larger interferometer, like one that could be in space, would
potentially be able to detect these
New Ways to Look at the Universe
With these discoveries, we can now study and observe:
– Ultra-massive black hole orbits and mergers: quasars at
the centers of galaxies had to get that big somehow, and
often their low frequency gravitational emissions have
been impossible to detect
– Relic gravitational wave emissions from the Big Bang:
such emissions have also been hard to detect, but they
exist at all frequencies and can offer us a better
understanding of the universe.
Frequencies
Source: Minglei Tong
Connection to Other Waves?
• On the same day as LIGO’s discovery, Fermi, a
gamma way detector, detected a burst of
gamma rays 0.4 seconds after the gravitational
wave discovery
• Scientists are beginning to think that the events
might be connected, though that would be a
puzzling reality
Connected to Other Waves?
• Short gamma wave bursts allow scientists to see
hidden cosmic events, typically the mergers of
neutron stars, or neutron stars and black holes
• The idea of gamma waves being produced from
two black holes is controversial – the merger of
black holes is not supposed to generate light
Gamma Wave Emissions
Dying star producing gamma waves.
Gamma Waves
• Gamma waves produce the most energetic
type of light in the electromagnetic spectrum
• They are supposed to have very little to do
with black hole mergers: black holes are
expected to merge “cleanly,” and without
producing any light
Connected to Other Waves?
• If gravitational waves and gamma ray bursts are linked, scientists
will have to explain what could cause bursts of light in
correspondence with black hole mergers. The discovery of
gravitational waves combined with an understanding of gamma
wave bursts opens new questions about physics and the universe.
• This is a question that has not been considered before, and further
demonstrates how more observations of gravitational waves can
help us understand the universe better