High-Quality Photograph of a Black Hole



Black holes are an well-known effect that is consistent with Einstein's theory. Black holes are an extremely dense region of space where even light cannot escape. The premise of this phenomena is that a massive object bends space-time. If that massive object was extremely dense, it would ultimately bend space-time so that the walls of the dent are vertical. If a light beam is traveling and encounters the black hole, it will be bent at a consistently increasing angle so that it loops back upon itself and continues circling. It is now trapped. Objects of mass can be caught in the same way. When they spiral to the center they will be crushed to extreme density.





Swartzschild Radius
Formula

A black hole is formes when a star collapses to a diameter equivelant to or past its Swartzschild Radius. The Swartzschild radius is a ratio of a spherical object's mass to its radius. The formula(left): Rs is the Radius, G is Gravitational Constant, m is the mass of the object , and c  is the speed of light in a vaccum. To put this in proportion,  if the earth were to become a black hole, the mass would have to be contained within a 9 millimeter radius. However most black holes are not quite as small. The chart below shows a few examples of their massive size:

sincerely,

Space Cadet

Gravitational lensing



Einstein's Cross- example of lensing.

 Einstein's Relativity theory allows for certain effects that would not be possible according to the Newtonian theory. Because Gravity does not involve a force, massless objects can be affected. A straight beam of light, passing by a dent in space-time caused by a object of mass, will be bent to follow that geodesic path. The implication of this is a phenomena called gravitational lensing.

The main idea of Gravitational Lensing is if a massive object is in front of a star, or other bright object, the rays from the star will be bent around the massive object, appearing to the observer to be two or more distinct objects.

This is far from being just an interesting effect. Using geometry, one can derive the approximate distance of the object. Also Astronomers are using gravitational lensing to predict the placement and size of pockets of dark matter, as it also bends light.
Sincerely,
Space Cadet

Newton and Einstein- Gravity

     In 1916, Einstein published his theory of General Relativity, radically changing the way we view gravity. Over 200 years earlier, Newton published his "law of universal gravitation" in Principia Mathematica. Newton's view of gravity held that gravity was a force. This force is the attraction of mass to mass, the larger mass having a stronger pull on the smaller mass, and the smaller mass pulled upon the larger with less force. To this day Newton's gravitational equation is used to approximate a given object's weight upon a given planet.

 However, Einstein saw gravity in a different light. He supposed that mass could bend the fabric of space-time, much like a bowling ball on a trampoline. A smaller mass, like a planet, would simply follow the geodesic curve in an acceleration percieved as a force.

Since 1916, Einstein's theory has been shown to be accurate over the years, as certain  points are proven, such as the GP-B probe and the proof that gravity acts at the speed of light. His theory also covers other important points (such as Gravitational lensing) to be mentioned in a later post.

Sincerely,

Space Cadet

Gravity Probe B - Testing Einstein's Theories

Gravity Probe B has tested- and proven,  two effects of the general relativity theory developed by Albert Einstein developed in 1916. Orbiting around the earth, the spacecraft has the perfect opportunity to measure this, as the earth itself is a large enough mass to warp space-time noticably. The sensitive gyroscopic sensors were able to prove:
"1.The geodetic effect—the amount by which the Earth warps the local spacetime in which it resides.


2.The frame-dragging effect—the amount by which the rotating Earth drags its local spacetime around with it."(GP-B Mission)
The Geodetic effect is an essential component of the General Relativity theory, as it rests upon the tenet that mass can warp space-time. This allows for the existence of black holes, quasars, and other space phenomena.
The frame dragging effect had never been tested before. It can be visualized as a ball spinning in a bowl of a thick liquid such as syrup. As it spins it drags the syrup in a spiral around it.
In theory testing relativity is a simple concept. According to GP-B Mission;
 
"1.Place a gyroscope and a telescope in a polar-orbiting satellite, 642 km (400 mi) above the Earth. (GP-B actually uses four gyroscopes for redundancy.)


2.At the start of the experiment, align both the telescope and the spin axis of each gyroscope with a distant reference point—a guide star.

3.Keep the telescope aligned with the guide star for a year, as the spacecraft makes over 5,000 orbits around the Earth, and measure the change in the spin-axis alignment of each gyro over this period in both the plane of the orbit (the geodetic precession) and orthogonally in the plane of the Earth's rotation (frame-dragging precession).

The predicted geodetic gyro-spin-axis precession is a tiny angle of 6,606 milliarcseconds (0.0018 degrees) in the orbital plane of the spacecraft. The orthogonal frame-dragging precession is a minuscule angle of 39 milliarcseconds (1.1x10-5 degrees). "
Links:
Official Site
NASA GP-B Mission
Paper model of the Spacecraft

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sincerely, Space Cadet