- 4083 - GRAVITATIONAL LENSING - measures galaxy mass? Gravitational lensing events are very rare, with one galaxy in a thousand unveiling the phenomenon. Since quasars are seen in about one every thousand galaxies a quasar acting as a lens is one in a million. The scientists expect to detect hundreds of these lensing quasars with the ESA-NASA mission Euclid, to be launched this summer with a Falcon-9 SpaceX rocket.
-------- 4083 - GRAVITATIONAL LENSING - measures galaxy mass?
- A massive galaxy
cluster in the constellation Cetus dominates the center of this image from the
NASA/ESA Hubble Space Telescope. This image is populated with a serene
collection of elliptical and spiral galaxies, but galaxies surrounding the
central cluster—which is named SPT-CL J0019-2026—appear stretched into bright
arcs, as if distorted by a gargantuan magnifying glass.
-
- This cosmic
contortion, called a “gravitational lens”, occurs when the powerful
gravitational field of a massive object like a galaxy cluster distorts and
magnifies the light from background objects. These objects would normally be
too distant and faint to observe, but the magnifying power of the gravitational
lens extends Hubble's view even deeper into the universe.
-
- This particular
galaxy cluster lies at a vast distance of 4.6 billion light-years from
Earth. Astronomers have found a way to
use this phenomenon of strong gravitational lensing to determine with
precision—about three times more precise than any other technique—the mass of a
galaxy containing a quasar, as well as their evolution in cosmic time. Knowing
the mass of quasar host galaxies provides insight into the evolution of
galaxies in the early universe, for building scenarios of galaxy formation and
black hole development.
-
- The masses of host
galaxies have been measured in the past, but with gravitational lensing, this
is the first time that the measurement is so precise in the distant
universe. A quasar is a luminous manifestation
of a supermassive black hole that accretes surrounding matter, sitting at the
center of a host galaxy. It is generally difficult to measure how heavy a
quasar's host galaxy is because quasars are very distant objects, and also
because they are so bright that they overshine anything within their vicinity.
-
- Gravitational
lensing allows us to compute the mass of the lensing object. Thanks to
Einstein's theory of gravitation, we know how massive objects in the foreground
of the night sky—the gravitational lens—can bend light coming from background
objects. The resulting strange rings of light are actually distortions of the
background object's light by the gravitational lens.
-
- Combine the
two—quasars and gravitational lensing—to measure the mass of a quasar's host
galaxy. The Sloan Digital Sky Survey
(SDSS) database was a great place to search for gravitational lensing quasars
candidates. In 2010 the Hubble Space Telescope observed four candidates of which
three showed lensing. Of the three, one stood out due to its characteristic
gravitational lensing rings: SDSS J0919+2720.
-
- The HST image of
SDSS J0919+2720 shows two bright objects in the foreground that each act as a
gravitational lens, two galaxies in the process of merging. The one is a bright quasar, within a host
galaxy too dim to be observed. The other bright object is another galaxy, the
main gravitational lens. A faint object on the far left is a companion galaxy.
The characteristic rings are deformed light coming from a background galaxy.
-
- By carefully
analyzing the gravitationally lensed rings it is possible to determine the mass
of the two bright objects… in principle.
One of the biggest challenges in astrophysics is to understand how a
supermassive black hole forms. Knowing
its mass, how it compares to its host galaxy and how it evolves through cosmic
times, are what allows us to discard or validate certain formation theories.
-
- In the local
universe, we observe that the most massive galaxies also host the most massive
black holes at their center. This could suggest that the growth of galaxies is
regulated by the amount of energy radiated by their central black hole and
injected into the galaxy.
-
-
July 9, 2023 GRAVITATIONAL LENSING
- measures galaxy mass? 4083
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Sunday, July 9, 2023
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