Astro 4 jae's final

Black holes can be detected through their interactions with surrounding matter. Key methods include:
X-ray Emissions: When a black hole accretes matter, the infalling material heats up and emits X-rays.
Gravitational Influence: Observing the motion of stars or gas clouds orbiting an unseen massive object.
Gravitational Waves: Detecting ripples in spacetime from black hole mergers.
Event Horizon Telescope (EHT): Imaging the black hole's shadow, as done with M87*.

The size of the source must be smaller than the distance light can travel in one week. Since light travels roughly 3×10103×1010 cm/s:
Size≲1 light week≈1.8×1012 kmSize≲1 light week≈1.8×1012 km
This constraint arises because variations in brightness cannot propagate faster than light.

Disk: A flattened, rotating structure containing most of the galaxy's stars, gas, and dust. It's where the spiral arms are located.
Bulge: A dense, spheroidal region at the center of the galaxy containing older stars.
Halo: A roughly spherical region surrounding the disk and bulge, containing old stars, globular clusters, and dark matter.

Hubble identified Cepheid variable stars in nearby galaxies and used the period-luminosity relation:
Measure the Cepheid's pulsation period.
Determine its intrinsic luminosity using the period-luminosity relation.
Compare intrinsic luminosity to apparent brightness to calculate distance via the inverse-square law.

An L∗L∗ galaxy refers to a galaxy with a luminosity approximately equal to the characteristic luminosity at the break in the galaxy luminosity function. In simpler terms, it represents a typical, bright galaxy like the Milky Way, around which the luminosity distribution of galaxies peaks.

The Universe is considered homogeneous on scales larger than about 100 Mpc (megaparsecs). At these scales, matter and energy are uniformly distributed, with no significant clumping of galaxies or other structures.

Approaching objects: Light is blue-shifted (wavelengths decrease).
Receding objects: Light is red-shifted (wavelengths increase).
The amount of shift depends on the velocity of the object relative to the observer.

Broad emission lines indicate that the gas in the vicinity of the AGN is moving at very high velocities. These velocities, often thousands of km/s, are due to the strong gravitational influence of the supermassive black hole at the center of the AGN.

During a lunar occultation, as the Moon passes in front of a distant object:
The object's light is temporarily blocked.
The precise timing of disappearance and reappearance of the light allows for highly accurate position measurements.
The exact location depends on the Moon's known position and the geometry of the event.

Extreme Luminosity: AGN can outshine entire galaxies, requiring an incredibly efficient energy source like accretion onto a supermassive black hole.
Small Size: Variability on short timescales (hours to days) implies a compact emitting region.
Rapid Variability: Indicates that the central engine is small, as the time for light to cross the emitting region is short.
Wide Wavelength Range: AGN emit across the electromagnetic spectrum, from radio to gamma rays.
Radio Jets: Some AGN produce powerful, relativistic jets observed in radio wavelengths.

Superluminal motion occurs when a relativistic jet, moving close to the speed of light, is pointed nearly in the direction of the observer. The apparent velocity exceeds the speed of light due to the combination of high speed and the angle of observation relative to the line of sight.

In the unified model of AGN, the broad-line region may be obscured by a dusty torus when viewed edge-on. Thus, only narrow lines are visible.

Hubble compared the recessional velocity (determined from redshifts) and the distance (determined using Cepheid variables) of galaxies.

A larger Hubble constant implies a faster expansion rate and a younger Universe, while a smaller value suggests a slower expansion and an older Universe.

Redshifts are due to the expansion of space, not the motion through space (as in the Doppler effect). Cosmological redshift stretches the wavelength of light as the Universe expands.

The Universe has expanded by 10% since the light left the galaxy.

Local galaxies are bound by gravity and can move towards each other despite the overall expansion of the Universe.

The observed duration is stretched by a factor of 1+z1+z. If the intrinsic duration is 1 month, we observe it as 1.5 months.

We observe their light from when they existed, as light from distant objects takes billions of years to reach us.

The cosmic microwave background (CMB) photons were emitted about 380,000 years after the Big Bang, during the era of recombination when the Universe cooled enough for neutral atoms to form, allowing photons to travel freely.

The CMB photons are still traveling through space and reaching us as remnants of the early Universe.

CMB Radiation
Expanding Universe (Hubble’s Law)
Abundance of Light Elements (Helium, Deuterium)
Large-Scale Structure of the Universe

They tracked the orbits of stars near the Galactic Center using infrared telescopes, determining the mass of the central object from the gravitational influence on the stars.

The Eddington limit sets the maximum luminosity a black hole can achieve before radiation pressure pushes back on infalling material.

Approximately 100 million years, assuming continuous accretion at the Eddington limit.

It is much lower than its full potential, as it is currently in a quiescent state with low accretion rates.

Such massive black holes would need to grow extremely rapidly, challenging models of black hole formation and early growth.

The object will follow a twisted trajectory due to the frame-dragging effect caused by the black hole’s spin.

A global network of radio telescopes that work together using very long baseline interferometry (VLBI) to image the event horizons of black holes.

The bright ring corresponds to the photon ring, where light is bent around the black hole, and the central dark region is the shadow of the event horizon.

The object stretches and compresses in alternating directions, although the effect is extremely small.

Emits radiation from radio waves to gamma rays.

Emits up to a trillion times the Sun's energy.

Emission originates from a region smaller than a light-month.

Changes in brightness over short timescales (days or weeks).

High-energy jets of matter ejected perpendicular to the accretion disk.

Narrow streams of particles moving near the speed of light.

A region of fast-moving gas near the black hole producing broad spectral lines.

A ring of cooler material surrounding the accretion disk.

Stretching of light wavelengths due to the expansion of space.

Wavelength changes caused by relative motion through space.

A Universe that looks the same in all directions.

Radiation from the early Universe, a remnant of the Big Bang.

Objects with predictable luminosity, used to measure distances.

A framework combining quantum mechanics and relativity to explain fundamental forces.

A mysterious force causing the accelerated expansion of the Universe.

A rotating disk of matter falling into a black hole, emitting intense radiation.

Apparent faster-than-light motion observed in relativistic jets due to projection effects.

Collisions between galaxies funneling gas to their centers.

Cooling of intergalactic gas, allowing it to fall toward a galaxy's center.

Explosions of white dwarfs that act as standard candles.

Early galaxies observed as they were billions of years ago.

A dense remnant of a massive star after a supernova, composed mostly of neutrons.

The central region of a galaxy emitting extraordinarily high energy, powered by accretion onto a supermassive black hole.

Compact energy source, broad spectral lines from gas moving at high velocities, and relativistic jets aligned with theoretical models of black hole magnetospheres.

The Broad Line Region (BLR) and dusty torus can block or reveal certain emissions depending on orientation.

Rapid fluctuations indicate a compact emission region, with variability timescales proportional to the size of the region (\(t = R/c\)).

Twisted magnetic fields near the black hole accelerate charged particles outward, forming high-energy jets.

Extreme luminosity, small size, rapid variability, wide wavelength range, and the presence of radio jets.

A supermassive black hole, accretion disk, broad line region (BLR), dusty torus, and relativistic jets.

Short variability timescales suggest a compact region, with size limited by \(t = R/c\).

Twisted magnetic fields near the black hole accelerate particles to near-light speeds, forming narrow jets that emit synchrotron radiation.

Apparent faster-than-light motion observed in relativistic jets occurs due to projection effects from jets moving close to the speed of light toward Earth.

Galaxy mergers, bars in spiral galaxies, and cooling flows funnel gas to the central black hole.

Hubble’s Law states that a galaxy’s recession velocity is proportional to its distance

A larger Hubble constant means a younger Universe.

Cosmological redshift is caused by the stretching of space, while the Doppler effect arises from motion through space.

Type Ia supernovae have predictable brightness, allowing accurate cosmic distance measurements.

A homogeneous and isotropic Universe, cosmic microwave background (CMB), and observations of distant galaxies and Type Ia supernovae.

The CMB comes from photons released 380,000 years after the Big Bang when electrons and protons combined to form neutral hydrogen.

Extremely luminous AGN from the early Universe, representing the growth phase of supermassive black holes and helping study early galaxy formation.

Abundant gas and frequent galaxy mergers in the dense early Universe fueled quasar activity.

Ripples in spacetime caused by accelerating massive objects, like merging black holes or neutron stars.

They stretch and compress due to spacetime distortion.

It confirmed black hole mergers and provided direct evidence of gravitational waves, validating Einstein's theory of general relativity.

It combines quantum mechanics and relativity to explain fundamental forces, dark energy, and the Universe’s evolution.

It causes the accelerated expansion of the Universe, driving the Big Freeze scenario.

Observations of dark energy and the Universe’s accelerating expansion.

Broad line regions can be obscured by the dusty torus depending on the viewing angle.

He compared the recession velocity and distance of galaxies to determine the relationship described by Hubble’s Law.

A redshift of 10% implies the Universe has expanded by 10% since the light left the galaxy.

It occurred everywhere in the Universe as space itself expanded.

The CMB’s photons have been traveling through space, reaching us as faint microwave radiation.

By observing light that has taken billions of years to travel to us, we see these galaxies as they were in the distant past.

Black holes of this size would require rapid growth unlikely to occur through stellar mass black hole mergers alone.

It uses light from the accretion disk bent around the black hole’s event horizon to create images of the shadow.

A phenomenon where tidal forces near a black hole stretch objects into long, thin shapes.

Really good at measuring mergers between very big black holes, but not with smaller ones, so x rays help with the smaller ones

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