رصد ثقب اسود مفرط الكتلة، وكتلته تساوي تقريبا 33 مليار ضعف كتلة الشمس
رصد ثقب أسود مفرط الكتلة باستخدام عدسة جاذبية قوية، وكتلته تساوي تقريبا 33 مليار ضعف كتلة الشمس، ويقع في مركز مجرة على بعد مئات الملايين من السنين الضوئية من الأرض
“Bayesian model
comparison favours a point mass with
MBH = 3.27 ± 2.12 × 1010 M⊙ (3σ confidence limit); an ultramassive black
hole.
This model still provides an upper
limit of MBH ≤
5.3 × 1010 M⊙”
تعريفات:
ثقب
أسود فائق الكتلة Supermassive Black Hole SMBH
ثقب اسود مفرط الكتلة
Ultramassive Black Hole UMBH
Research paper:
Abell 1201: detection of an ultramassive
black hole in a strong gravitational lens,
J W Nightingale et al,
Monthly Notices of the Royal
Astronomical Society, Volume 521, Issue 3, May 2023, Pages 3298–3322,
https://doi.org/10.1093/mnras/stad587
Published: 29
March 2023
Abstract:
Supermassive black holes (SMBHs) are a key catalyst of galaxy formation and evolution, leading to an observed correlation between SMBH mass MBH and host galaxy velocity dispersion σe. Outside the local Universe, measurements of MBH are usually only possible for SMBHs in an active state: limiting sample size and introducing selection biases. Gravitational lensing makes it possible to measure the mass of non-active SMBHs. We present models of the z = 0.169 galaxy-scale strong lens Abell 1201. A cD galaxy in a galaxy cluster, it has sufficient ‘external shear’ that a magnified image of a z = 0.451 background galaxy is projected just ∼1 kpc from the galaxy centre. Using multiband Hubble Space Telescope imaging and the lens modelling software PYAUTOLENS, we reconstruct the distribution of mass along this line of sight. Bayesian model comparison favours a point mass with MBH = 3.27 ± 2.12 × 1010 M⊙ (3σ confidence limit); an ultramassive black hole. One model gives a comparable Bayesian evidence without an SMBH; however, we argue this model is nonphysical given its base assumptions. This model still provides an upper limit of MBH ≤ 5.3 × 1010 M⊙, because an SMBH above this mass deforms the lensed image ∼1 kpc from Abell 1201’s centre. This builds on previous work using central images to place upper limits on MBH, but is the first to also place a lower limit and without a central image being observed. The success of this method suggests that surveys during the next decade could measure thousands more SMBH masses, and any redshift evolution of the MBH−σe relation. Results are available at https://github.com/Jammy2211/autolens_abell_1201.
Monthly Notices of the Royal
Astronomical Society, Volume 521, Issue 3, May 2023, Pages 3298–3322,
https://doi.org/10.1093/mnras/stad587
Published: 29
March 2023
Gravitational lensing
Gravitational lensing is a
phenomenon in which the gravitational field of a massive object, such as a
galaxy or a black hole, bends and distorts the path of light rays passing
nearby. This distortion of light can cause distant objects to appear magnified,
distorted, or even multiplied.
The most common type of
gravitational lensing is known as strong lensing, which occurs when the
path of light is significantly curved, resulting in multiple images of the same
object. Another type of lensing, called weak lensing, is much subtler
and only produces a slight distortion of the shapes of distant galaxies.
Gravitational lensing is a
powerful tool for astronomers to study distant and faint objects in the
universe that would otherwise be impossible to observe. By analyzing the way
that light is bent by a massive object, scientists can learn about the
distribution of matter in the lensing object, including the amount and
distribution of dark matter, as well as the mass and structure of the lensed
object.
One of the most famous examples of gravitational lensing is the Einstein Cross, a quasar that appears as four distinct images due to the lensing effect of a foreground galaxy.
The formula for gravitational lensing is given by the lens equation:
β = θ - (D_LS/D_S) α
β is the angular position
of the lensed object (the source) relative to the lensing object (the lens) in
the sky.
θ is the angular position
of the source as it would appear in the absence of the lens.
D_LS is the angular
diameter distance between the lens and the source.
D_S is the angular
diameter distance between the observer and the source.
α is the deflection angle
of the light ray by the lens.
The lens equation relates
the apparent position of the source (β) to its true position (θ) and the deflection
angle of the light ray (α), which depends on the mass distribution of the lens.
The ratio of the angular diameter distances D_LS and D_S determines the
strength of the lensing effect.
The lens equation can be used to predict the positions and magnifications of lensed images, as well as to infer the mass and structure of the lensing object from the observed lensed images.
The lensing equation can
also be derived from the general theory of relativity, which describes the
curvature of spacetime by massive objects.
In the weak-field limit, the gravitational field can be described by a metric tensor g, which is a mathematical object that encodes the curvature of spacetime. The geodesic equation, which describes the motion of a test particle in a gravitational field, can be written as:
d^2x^μ/dτ^2 + Γ^μ_νρ dx^ν/dτ dx^ρ/dτ = 0
For light rays, which travel on null geodesics (ds^2=0), the equation becomes:
d^2x^μ/dλ^2 + Γ^μ_νρ dx^ν/dλ dx^ρ/dλ = 0
where λ is an affine
parameter along the null geodesic.
By assuming a weak gravitational field and a static, spherically symmetric lens, the metric tensor can be written as:
ds^2 = -(1 + 2Φ/c^2) c^2 dt^2 + (1 - 2Φ/c^2) (dx^2 + dy^2 + dz^2)
where Φ is the
gravitational potential of the lens, c is the speed of light, and t is the time
coordinate.
Using this metric tensor, the deflection angle of a light ray passing near the lens can be calculated to be:
α = 4GM/c^2 r
Substituting this deflection angle into the lens equation β = θ - (D_LS/D_S) α, where θ is the apparent position of the source and D_LS and D_S are the angular diameter distances, yields the same result as the weak-field approximation of the lens equation from classical physics.
Ammar Sakaji,
President of the
Jordanian Astronomical Society JAS
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