Astro 4 better final

Spaghettification is the process by which objects are stretched and elongated due to the extreme tidal forces near a black hole. As the object approaches the black hole, the gravitational pull on its nearer side is much stronger than on its farther side, causing it to be stretched into a thin, elongated shape resembling spaghetti.

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.

They have a consistent peak luminosity, allowing distance measurements based on their apparent brightness.

The Big Bang happened everywhere in the Universe simultaneously, as it was the beginning of space and time.

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

Quasars were more common when galaxies and their central black holes were forming and had abundant gas to fuel accretion.

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.

These black holes likely formed from massive stars or prior mergers, leading to higher initial masses.

Suction is the result of a pressure difference. Lower pressure inside a system causes external atmospheric pressure to push fluids or objects toward the lower-pressure region.

Quarks are fundamental particles that combine to form protons (2 up, 1 down) and neutrons (1 up, 2 down).

In string theory, particles are different vibrational modes of tiny strings, with each mode corresponding to a specific particle.

A theoretical prediction that black holes emit radiation due to quantum effects near the event horizon, causing them to lose mass over time.

The rate of Hawking radiation is extremely slow, and for most black holes, this loss is negligible compared to their mass.

A graphical representation of particle interactions, showing how particles exchange force carriers over time.

A quantum field that permeates space, with electrons being excitations of this field.

Antimatter consists of particles with opposite charges and quantum numbers to their matter counterparts (e.g., positron is the antimatter of the electron).

Primordial Age: Big Bang energy.
Stelliferous Age: Fusion in stars.
Degenerate Age: Residual heat in stellar remnants.
Black Hole Age: Hawking radiation.
Dark Era: Faint radiation from remaining particles.

White dwarfs, neutron stars, and other stellar remnants.