Matter in the Universe

Matter is generally considered to be anything that has mass and volume. The volume is determined by the space in three dimensions that it occupies. The mass is determined by its rest mass (or invariant mass), which is measured by the acceleration a body has when a force is applied. The greater the mass, the slower the acceleration for the same force. Matter is thus a general term for the substance of which all observable physical objects consist

The matter in the universe is created by the big bang, but not in the form that we see today. First, there is very strong evidence that most of the matter in the Universe is in the form of unseen or dark matter - matter that (at least so far) cannot be seen by standard astronomical methods, but whose presence can be inferred because it influences the Universe gravitationally. The nature of this dark matter is one of the most important unsolved problems in science.
Second, the big bang produces mostly the light elements hydrogen and helium (Here is a java applet illustrating big bang synthesis of the elements). The heavier elements must be produced later, by stars. Furthermore,

1. Many of the heavier elements cannot be produced by stars in the stable periods of their lives - they must be produced in violent explosions associated with the death of stars.
2. The heavier elements produced either in the stable portion of stellar evolution, or in violent explosions, can only be distributed through the universe by such explosions.

Thus, the existence of the heavy elements, and the biology built on them, depends crucially on violent processes taking place in stars and galaxies.

Read More...

Cosmology

Cosmology is the study of the larger issues: how "big" is the Universe, does it have an "end", what is its large-scale structure, how old is the Universe, how long will it live?

Cosmology is the study of the origin and the development of the Universe. As such, it is concerned with the large scale, both with respect to distance, and with respect to the past and future for the Universe.

The Central Themes of Modern Cosmology

The central tenet of modern cosmology is the idea that the Universe is expanding, and that this implies that at some time in the distant past it was incredibly dense and hot. This "explosion" from a hot, dense initial state is called the big bang (or sometimes the hot big bang, to emphasize the high temperature during its occurrence). Some of the most important problems in cosmology are associated with understanding how galaxies and clusters of galaxies formed, and determining the nature of the mass of the Universe (we can only identify 10 percent of what we know from its gravitational influence must be there!).

Read More...

Motion of the Sun

The Sun is in motion, just like any other star.

Motion of the Sun Relative to Local Stars

First, the Sun and the other stars in its vicinity partake of the general rotation of the galaxy (the Milky Way Galaxy rotates once about every 225 million years). This corresponds to an average velocity of about 220 km/s. The space velocities that we measure for other stars then correspond to deviations from this average motion for the stars around the Sun. This happens because the Sun and the stars near it are on somewhat different orbits around the center of the galaxy, so at any one time the Sun is overtaking some stars and being passed by others.

The Solar Apex and Antapex

This motion of the Sun with respect to the local field of stars is in the direction of an imaginary point in the constellation Hercules, near the bright star Vega. This point is called the solar apex, and the Sun is moving toward it (relative to the nearby stars) at a net speed of about 19.7 km/s. The point on the opposite side of the sky from which the Sun appears to be moving away is called the {\em solar antapex}.
Thus, every second we move about 20 km closer to the star Vega. However, there is plenty of time before we get there: Vega is 26.5 light years away! As an exercise, calculate how long it will take the Sun (and therefore the Earth) to travel 26.5 LY at a speed of 20 km/s.

Read More...

Limitations of the Human Eye

The human eye is a remarkable biological invention, a shining triumph of the process of evolution. Although the human eye was the detector that started us on mankind's exploration of the Cosmos, it has some shortcomings that ultimately limit that exploration:

1. The eye has limited size and therefore limited light-gathering power.
2. The eye has limited frequency response, since it can only see electromagnetic radiation in the visible wavelengths.
3. The eye distinguishes a new image multiple times a second, so it cannot be used to accumulate light over a long period in order to intensify a faint image.
4. The eye cannot store an image for future reference like a photographic plate can.

Astronomers have developed a variety of instruments and techniques to supplement the human eye and to alleviate these shortcomings. As a result, in modern research astronomy, very few observations are made any more by an astronomer looking directly through an optical telescope.

Read More...

Planet found in nearest star system to Earth

This artist’s impression shows the planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Alpha Centauri B is the most brilliant object in the sky, and the other dazzling object is Alpha Centauri A. Our own Sun is visible to the upper right. The tiny signal of the planet was found with the HARPS spectrograph on the 3.6-meter telescope at ESO’s La Silla Observatory in Chile. // Credit: ESO/L. Calçada/N. Risinger

The observations extended over more than four years using the HARPS instrument and have revealed a tiny signal from a planet orbiting Alpha Centauri B every 3.2 days.

 European astronomers have discovered a planet with about the mass of the Earth orbiting a star in the Alpha Centauri system — the nearest to Earth. It is also the lightest exoplanet ever discovered around a star like the Sun. The planet was detected using the HARPS instrument on the 3.6-meter telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

Alpha Centauri is one of the brightest stars in the southern sky and is the nearest stellar system to our solar system, only 4.3 light-years away. It is actually a triple star — a system consisting of two stars similar to the Sun orbiting close to each other, designated Alpha Centauri A and B, and a more distant and faint red component known as Proxima Centauri. Since the 19th century, astronomers have speculated about planets orbiting these bodies, the closest possible abodes for life beyond the solar system, but searches of increasing precision had revealed nothing. Until now.

"Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days," said Xavier Dumusque from the Geneva Observatory in Switzerland and the University of Porto in Portugal. "It's an extraordinary discovery, and it has pushed our technique to the limit!"

The European team detected the planet by picking up the tiny wobbles in the motion of the star Alpha Centauri B created by the gravitational pull of the orbiting planet. The effect is minute. It causes the star to move back and forth by no more than 20 inches (51 centimeters) per second, about the speed of a baby crawling. This is the highest precision ever achieved using this method.

Alpha Centauri B is very similar to the Sun but slightly smaller and less bright. The newly discovered planet, with a mass of a little more than that of Earth, is orbiting about 3.7 million miles (6 million kilometers) away from the star, much closer than Mercury is to the Sun in the solar system. The orbit of the other bright component of the double star, Alpha Centauri A, keeps it hundreds of times farther away, but it would still be a brilliant object in the planet's skies.

This same team found the first exoplanet around a Sun-like star in 1995, and since then there have been more than 800 confirmed discoveries, but most are much bigger than Earth, and many are as big as Jupiter. The challenge astronomers now face is to detect and characterize a planet of mass comparable to Earth that is orbiting in the habitable zone around another star. The first step has now been taken.

"This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star, and it must be much too hot for life as we know it," said Stephane Udry from the Geneva Observatory, "but it may well be just one planet in a system of several. Our other HARPS results and new findings from Kepler both show clearly that the majority of low-mass planets are found in such systems."

"This result represents a major step towards the detection of a twin Earth in the immediate vicinity of the Sun. We live in exciting times!" said Dumusque.

Read More...