User:Serendipodous/indigo/page 7

page 6 page 8

Black Holes
Contrary to popular belief, Einstein was neither bad at math nor a bad student (he passed with a grade of, essentially, 5 out of 6), but he was insufferably disrespectful to his teachers. Likely due to their bad reccommendations, he failed to get a job at any Uiversity. He had several odd jobs until, in 1902, he gained the title of "technical expert, thrid class" at the Swiss Patent Office in Bern.

The speed of light is constnat in all reference frames.

1881 and 1887: Michaeso-morley show that lightspeed is constat in all directions.

Physicists agreed that the experiment was carefully executed and well desiged, and that the result was unlikely to be the result of error- other physicists, such as Einsteins teacher Heirich Weber, believed that Newtonian physics would triumph in time.

In SR, you speeding by see me slow down, and I see you slow down.

Einstein had no measuring tool to prove his hypothesis; there was little experimental data to work with- his conclusion was based on his own intuition.

reference frames and gravity

principle of equivalence.

Weeks later, he received a letter from Max Planck asking for clarification. He had expected vicious criticism and controversy but got silece.

Cotroversy would evetually take hold, and lasted for two decades, eve after he received the Nobel Prize i 1922. Relativity was not the reason why.

When techology finally caught up with Einstein in the 1930s, cotroversy died dow

Herman Minkowski, named einstein a lazy dog as a student- eistein saw spacetime as a mathematical consturct that obscured physical reality and joked about it. He was wrong.

1908: Einstien gave up on gravity by 1911, was made a full professor at Prague.

he hated lecturing on topics he wasn't interested in - eventually moved to Berlin, where he had no teaching duties

1915- ten years after special relativity, einstein finally cracked general relativity

Einstein struggled to uderstand reimann geometry, and presented many incorect proposals to the Prussian Academy of sciences in Berlin before noticing mistakes and revisng his equations

Einstein field equation

"Schwarzchild sigularities do not exist in physical reality" Einstein 1939

1783 John mitchell, rector at thornhill in Yotrkshire: Escape velocity is proportional to the square root stars mass dividedby the circumference. the smaller the circumference, the clsoer the surface to the centre of the star's mass,a and the higher the escape velocity- dark stars

Wave theroy of light began to suppplant particle theroy, and th question of whether light could be affected by gravity ebcame unclear.

1915: Karl Schwartzchild calcualted the spacetime curvature of any spherical object Schwartzchiold geometry while serving o the Russia frot in WWI. In 1916, he calculated the spacetinme geometry inside a star, but died from illness shorty after,

schwarzchild geometry predicted a critical circumference (18.5 km x star's mass) time dilation and redshifting of light, is infinite.

this is different from the Newtonian idea of a black star: in Newtonian physics, the speed of light is relative; at just below the radius,light would propagate for a while, then gradually be pulled back in. anyone in orbit around the star could still see it, but we could not. But in einsteinian physics the speed of light is absolute- The light ceases to exist beyond the event horizon.

electron degeracy pressure: When electrons are compressed to 10,000 times their normal space, they begin to move erratically; wave particle duality creates high-wavelength, and high energy particles. These are not affected by loss in temperature.

19 year old chandrasekhar on a ship to cambridge worked out that a white dwarf with more than 1.4 times the mass of the Sun could not support itself against its own gravity. because to increase the resistance any further the electrons gain so much relativistic mass that their speeds slow and their resistance decreases.

Even though they accepted Chandra's numbers (behind eddington's back) they still believed that some law of nature must prohibit the collapse into anything denser, perhaps expulsion of matter during supernovae.

oppenheimer volkoff limit for neutron stars

One could never see a star collapse into a black hole from orbit, because of grativational time dilation

The term "black hole" was coined by wheeler in 1967 (or maybe not)

Black holes pulsate; gravitational waves within the vacinity of a black hole are indistinguashable from pulsations, since both are ripples in spacetime curvature

When a black hole is formed all one can learn about the star it once was is its spin, electrical charge and mass

Black holes create "tornadoes" of spacetime near their horizons

An observer experiences a finite and short span of time after crossing an event horizon, while an infinite amount of time passes outside it.

A black hole cannot spin fast enough to tear itself apart; something always gets in the way

In 1969 Roger Penrose realised that black holes store rotational energy in the spacial tornadoes they produce, which could be extracted for power. This energy extraction would be 48 times more efficient than the Sun.

To find dense stars, the best method, determined by Zel'dovich, was to look for superheated gas from stellar winds intercepted by black holes- heated to several million degrees, it would shine mainly in X-rays. X-rays are (thankfully) blocked by our atmosphere so one has to get above the atmosphere to find them.

The first X-ray "telescope" was launched on top of a rocket from White Sands missile range in NM and rose to an altitude of 250 km. It took x-ray readings for 350 seconds, found a massive x-ray source in the constellation Scorpius that was 5000 times more intense then predicted.

Eventually, X-ray telescopes were launched that allowed for visual precision akin to the best optical telescopes. Neutron stars, stellar coronae, supernova remains, hot interstellar gas and, of course, potential black holes

In 1974, Stephen Hawking and Kip Thorne made a bet over one of the most promising black hole candidates, Cygnus X-1. Hawking said no, Thorne said yes. Thorne asked for a Penthouse magazine subscription, Hawking for Private Eye. In 1990, 16 years later, Hawking, accompanied by his family and nurses, in Thorne's words "broke into" his office at Caltech and officially conceded, signing a concession with his thumbprint.

Cygnus X-1 is an optically dark but x-ray bright object orbiting an optically bright but x-ray dim star, just as predicted by Zel'dovich and Novikov, and is over the size limit to be a neutron star. It is overwhelmingly likely a black hole.

The first evidence for a black hole was found by Karl Jansky, an employee at Bell Telephone, who was looking for a way to limit radio static in trans-atlantic phone conversations. In 1935 he identified a massive radio source at the centre of our galaxy. When the central region was overhead, it was strong, when it went below the horizon, it dimmed. This radio source was brighter than our own Sun. According to current astrophysical theory, this was impossibe.

Before the war, institutions had no interest in radio astronomy. Grote Reber, a ham radio operator and "bachelor" built the first ever radio telescope in his mother's backyard. Radio map of the galaxy- cyg A and Cas A. He submitted a paper to Chandra, who was head of the Astrophysical Journal at the time, who circulated among his colleagues. After going down for a visit, they submitted it for publication.

After the war, physicists who had led the development of radar led the charge for radio astronomy

In 1949. the first radio signals were identified as coming from distant galaxies. Astronomers at first disbelieved the information and assumed that it must be from a nearer source in our own galaxy.

In 1951, radio precision had increased 10-fold and Walter Baade confirmed the existence of "radio galaxies" like Cyg A optically.

In 1960, Jodrel Bank notified Tom Matthews of Caltech of an unusually small radio source, when the coordinates were handed to alvin standage of the Carnegie Institute, he found a tiny bright piont of light that resembled a star, though its spectrum was unlike anything ever seen before.

In 1962, Maartin Schmidt, a Dutch emigre at caltech, figured out that the spectrum was in fact that for hydrogen gas, but redshifted as far as 16 percent. This meant it had to be moving away from earth at 16 percent the speed of light. The only explanation for these massive redshifts was that these objects (later dubbed quasars) were very far away, and being dragged by the universe's expansion. The first two identified quasars were identified as being 2 billion and 4.5 billion light years away, the largest distances yet measured, and thus must be sources of immense power, emitting 100 times as much energy as a galaxy.

Observations showed that light from these object sometimes fluctuated over the course of a month, suggesting that the majority of light from these strange objects must eminate from a source smaller than 1 "light month" in size. 10^18 times smaller in volume

The only force that conceivably produce that much energy is gravity. The implosion of 100 million normal stars or one hypothetical star with 100 million solar masses could do it. The idea of a supermassive black hole could create a high energy and 29 percent efficiency of the spining spacetime tornado were not known at the time.

Radio galaxies were known to have high-energy "lobes" that were revealed to be jets of matter extending out to millions of light years from the galaxtic centre. Only one object in theory could account for all the observed features, a spinning giant black hole.

David Lyndon Bell of Cambridge showed that the 1 light month source was likely an accretion disk of matter aroudn the black hole superheated by friction to millions of degrees.

how the jets form is not fully understood, though models have shown they could be generated by the intense heat radiating from the accretion disk, or from spinning magnetic field lines either from the disk or from the black hole itself, set them to swirl by the spacetime vortex.

Supermassive black holes may form from the gradual inward spiral of stars flung inward by stellar collisions, which eventually congregate in teh centre and implode into a black hole. friction in interstellar gas also sends it eventually to the core.

Inertial frame: frame in which the law of inertia holds- stationary or moving at a constant velocity Non-inertial frame: frame in which a body is accelerated, creating the illusion of force.

Misconceptions

Black holes are not real

black holes are flat

Black holes have infinite pulling power

Black holes have infinite mass

Black holes suck

black holes crush you

Nothing can escape a black hole

Hibernation
As the universe cools down, one Joule of energy is worth proportionally more. This can be a substantial (1030) gain.

This paper is very much based on the physical eschatology research direction started by Freeman Dyson

Dysonian SETI takes the approach to widen the search to look for detectable signatures of highly advanced civilizations, in particular megascale engineering.

an early civilization, after expanding to gain access to enough raw materials, will settle down and wait until it becomes rational to use the resources

If utility requires contact (e.g. true value is achieved by knowledge shared across a civilization) then these limits will strongly reduce the utility of expanding far outside a galactic supercluster.

It also appears likely that a sufficiently advanced civilization could regulate its “mental speed”,

high discount rates may prevent such long-range projects and hence only low-discount rate civilizations will be actors on the largest scales.

This is linked to a reduction of opportunity costs: advanced civilizations have mainly “seen it all” in the present universe and do not gain much more information utility from hanging around in the early era

Enceladus
Lemonick: The 40 foot telescope was too sensitive to temperature change- modern telescopes use thin mirrors with actuators to adjust to temperature, and took up too much valuable seeing time to set up. Herschel used his 20 foot to search for the moon and then the 40 foot to confirm.

Travis: 2015 Serpentine formation?

crater relaxation suggests enceladus has had episodic heating events in its history

4.7 to 15.8 gw, depending on the wavelength

Enceladus's density is just 1.6 that of water

0.8% ammonia, salt rich ice at base sodium chloride, sodium hydrogen carbonate and sodium carbonate

2014 doppler gravity data: south polar sea extending to 50° S

radiogenic heating could not keep enceladus warm for longer than, at most, 1.5 Gyr

Kite, Rubin 2016

As of 2016, the plumes at Enceladus's south pole have been erupting continuously- the E-ring has been stable since its discovery in 1966

30=-10 KM SHELL OVERLAYING A SUBSRUFACE OCEAN CONTAINING ARGON,

Enceladus was discovered on August 28, 1789, by William Herschel son john named after titans- perhaps a misnomer for the majority.

https://apod.nasa.gov/apod/ap170416.html

Previous analysis of Cassini data suggested the presence of a lens-shaped body of water, or sea, underlying the moon's south polar region. However, gravity data collected during the spacecraft's several close passes over the south polar region lent support to the possibility the sea might be global."

more than seven years' worth of images of Enceladus In 2015

Enceladus has a tiny, but measurable wobble [libration] as it orbits Saturn. Because the icy moon is not perfectly spherical -- and because it goes slightly faster and slower during different portions of its orbit around Saturn -- the giant planet subtly rocks Enceladus back and forth as it rotates.

"If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be,"

sixth largest moon, only 157 miles (252 km) in mean radius,

In 2005, Cassini's multiple instruments discovered that this icy outpost is gushing water vapor geysers out to a distance of three times the radius of Enceladus.

The particles and gas escape the surface at jet speed at approximately 800 miles per hour (400 meters per second). The eruptions appear to be continuous, refreshing the surface and generating an enormous halo of fine ice dust around Enceladus, which supplies material to one of Saturn's rings, the E-ring.

Several gases, including water vapor, carbon dioxide, methane, perhaps a little ammonia and either carbon monoxide or nitrogen gas make up the gaseous envelope of the plume.

e measurements suggested a large sea about 6 miles (10 kilometers) deep beneath the southern polar region, under an ice shell about 19 to 25 miles (30 to 40 kilometers) thick.

Enceladus's albedo is 0.99, higher even than fresh snow.

t. Because Enceladus reflects so much sunlight, the surface temperature is extremely cold, about -201 degrees C (-330 degrees F).

Saturn's E Ring, the outermost of its major rings, and is its main source.

Enceladus is, like many moons in the extensive systems of the giant planets, trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior, and possibly driving the geological activity.

Discovered in 1789 by William Herschel

The finding agrees with the results of a 2016 study by a team independent of the Cassini mission that estimated the thickness of Enceladus' icy crust. The studies indicate an average depth for the ice shell of 11 to 14 miles (18 to 22 kilometers), with a thickness of less than 3 miles (5 kilometers) at the south pole.

Finding temperatures near these three inactive fractures that are unexpectedly higher than those outside them

white smokers water rock interaction release molecular hydrogen; plumes contain substantial amounts of molecular hydrogen, a potential food source for methanogenic lifeforms

https://www.youtube.com/watch?v=-nzaFDkDU7c

A 2007 study predicted the internal heat of Enceladus, if generated by tidal forces, could be no greater than 1.1 gigawatts,[101] but data from Cassini's infrared spectrometer of the south polar terrain over 16 months, indicate that the internal heat generated power is about 4.7 gigawatts,[101] and suggest that it is in thermal equilibrium.[9][52][102] The observed power output of 4.7 gigawatts is challenging to explain from tidal heating alone, so the main source of heat remains a mystery.[4][97] Most scientists think the observed heat flux of Enceladus is not enough to maintain the subsurface ocean, and therefore any subsurface ocean must be a remnant of a period of higher eccentricity and tidal heating, or the heat is produced through another mechanism.[103][104]

Following Voyager's encounters with Enceladus in the early 1980s, scientists postulated that it may be geologically active based on its young, reflective surface and location near the core of the E ring.[41] Based on the connection between Enceladus and the E ring, scientists suspected that Enceladus was the source of material in the E ring, perhaps through venting of water vapor.[35][36]

The significantly higher density of Enceladus relative to Mimas (1.61 vs. 1.15 g/cm3), implying a larger content of rock and more radiogenic heating in its early history, has also been cited as an important factor in resolving the Mimas paradox

The presence of a subsurface ocean under the south polar region is now accepted,[92] but it cannot explain the source of the heat, with an estimated heat flux of 200 mW/m2, which is about 10 times higher than that from radiogenic heating alone.[93]

Several explanations for the observed elevated temperatures and the resulting plumes have been proposed, including venting from a subsurface reservoir of liquid water, sublimation of ice,[94] decompression and dissociation of clathrates, and shear heating,[95] but a complete explanation of all the heat sources causing the observed thermal power output of Enceladus has not yet been settled.

In 2016, a study of how the orbits of Saturn's moons should have changed due to tidal effects suggested that all of Saturn's satellites inward of Titan, including Enceladus (whose geologic activity was used to derive the strength of tidal effects on Saturn's satellites), may have formed as little as 100 million years ago.

In 2015, the Cassini probe made a close fly-by of Enceladus' south pole, flying within 48.3 km (30 mi) of the surface, as well as through a plume in the process. A mass spectrometer on the craft detected molecular hydrogen particles from the plume, and after months of analysis, the conclusion was made that the hydrogen was most likely the result of hydrothermal activity beneath the surface. It has been speculated that such activity could be a potential oasis of habitability.

Voyager 2 found several types of tectonic features on Enceladus, including troughs, scarps, and belts of grooves and ridges.[41] Results from Cassini suggest that tectonics is the dominant mode of deformation on Enceladus, including rifts, one of the more dramatic types of tectonic features that were noted. These canyons can be up to 200 km long, 5–10 km wide, and 1 km deep. Such features are geologically young, because they cut across other tectonic features and have sharp topographic relief with prominent outcrops along the cliff faces.

VIMS also detected simple organic (carbon-containing) compounds in the tiger stripes, chemistry not found anywhere else on Enceladus thus far.

A model suggests that Enceladus's salty ocean (-Na, -Cl, -CO3) has an alkaline pH of 11 to 12

observed heating of Enceladus is not enough to maintain a subsurface ocean for more than 30 million years (Enceladus is billions of years old)

Alexander, 1980
giovanni dominico Cassini discovered the rotations of Mars and Jupiter, identified their surface features. Professor of astronomy at Bologna from the age of 25 to 44, and mapped the motions of the galilean moons.

In 1669 he was invited by Louis XIV to head the new paris observatory, whereupon he became a french citizen and changed his name to Jean Dominique.

"This passage of Saturn gave occasion to discover in the same place, within the space of ten minutes, by a telescope of 17 feet .. eleven other smaller stars, one of which, by its particular motion showed itself to be a true planet, which we found by comparing it, not only to Saturn and its ordinary satellite discovered by Mr. Huygens in 1655. But also to other fixed stars etc.

1672, in his report confirming the second of his saturn satellite discoveries, later to be named rhea, Cassini noted a very strange fact about the behaviour of Iapetus: it appeared to grown and shrink in brightness at a very regular rate. Since this could not be due to the object moving farther away from the Sun, it had to be because "one part of his surface is not so capable of reflecting to us the light of the sun which maketh it visible, as the other part is."

1684: Dione and tethys

1787: WIlliam Herschel, 6 years post uranus, found two new satellites of saturn,

Herschel found that iapetus's brightness changed regularly with orbit. He found that iapetus's rotation period was equal to its revolution period, just like our moon's

Enceladus was instantly visible to 19th century telescopes, but Mimas frequently evaded detection

Mimas resonances coincided with the cassini division

Evans 2004
Rhea: Low gravity and ice led to unusually well-preserved craters, with sharp edges

Chasms ran through one set of craters, but not the second

Hyperion: the product of a massive impact- possibly the same impact that led to cratering on Rhea

Tethys and Mimas: largest craters in proportion to their size in the Solar System- possible victims of the second cratering event

Hershel has few craters on top of it

Tethys also has a large crater, odysseyus, which alone is wider than Mimas.

Ithaca Chasma

Mimas and Tethys are both made of almost pure ice

Enceladus brightest object in the soalr system 0.95 albedo

fresh ice, possible cryovolcanism, fault lines, few large craters, indicating no damage from early mass cratering events

tidal heating

co-orbital moons: Helene for Dione; Telesto and Calypso for Tethys

amata- wispy feature on dione, associated with troughs, possibly due to earlier geological activity no longer present

shepherd moons prometheus/pandora epimethius/janus