Saturday, April 24, 2010

Hubble's top five scientific achievements...

Gas pillars in the Eagle Nebula: One of Hubble's most famous images. Image courtesy NASA.

On May 19, 2009, the Space Shuttle Atlantis released the
Hubble Space Telescope (HST) back into orbit after a hugely successful servicing mission, during which two new instruments have been installed on board the telescope, and two existing ones have been repaired. This marked the beginning of the next phase in the life of this incredible observatory. During its 19 years of operation, HST has produced 39 terabytes of data in the HST archive. At the time of this writing, 7,917 refereed scientific articles have been written based on HST data. With such a record, it is clearly impossible to even just list the HST's scientific accomplishments in a short article. In what follows, I have attempted to briefly describe (in no particular order) what I regard as the top five scientific discoveries. I should also note that rarely do astronomical discoveries belong to just one telescope. Usually it is many observatories, from the ground and from space, working in concert to produce a complete and multihued view of phenomena. Nevertheless, in the topics that I have selected, there is no doubt that HST played a crucial role.

The Hubble Constant
The astronomer
Edwin Hubble, after whom the Hubble Space Telescope is named, determined in the 1920s that our Universe is expanding. The fabric of space between any two distant galaxies is stretching, just like the rubber of an inflating balloon. The rate at which galaxies are currently moving apart from one another is known as the Hubble constant, or H0. For a constant rate of expansion, the inverse of H0 gives the time at which the expansion started. But even in the presence of deceleration and acceleration H0 is the dominant factor in determining the age of the Universe.
Before HST, the value of H0 was known only to within a factor of two. The main reason for this large uncertainty was the fact that the determination of distances in astronomy is notoriously difficult. To overcome this obstacle, astronomers have constructed a distance ladder in which they use a series of standard candles — objects whose brightnesses are relatively well known — to infer distances to objects that are increasingly farther away.
Figure 1: Cepheid variable star in galaxy M100. Image courtesy NASA.

Key standard candles are certain pulsating stars — stars that show periodic variations in their brightness — known as Cepheid variables. These are luminous stars, about a thousand times more luminous than the Sun, whose intrinsic brightness is tightly correlated to their pulsation period. By measuring the period of the variation, astronomers deduce the intrinsic brightness, and by comparing that to the apparent brightness, they can determine the distance (the apparent brightness decreases like the inverse square of the distance). The superb resolution of HST has allowed astronomers to isolate the light from numerous Cepheids in dozens of galaxies (figure 1), and the uncertainty in the value of the Hubble constant has initially been reduced to about 10%. Most recently, detailed HST observations of Cepheids in the galaxy NGC 4258 — whose distance is very accurately known through radio observations — coupled with observations of well-calibrated supernova explosions in more distant galaxies, have reduced the error in the value of H0 to less than 5%.

Dark Energy
In 1998, two teams of astronomers working independently discovered that the expansion of our Universe is in fact speeding up, propelled by the repulsive force of a mysterious dark energy. This came as a shock, because the prevailing assumption was that cosmic expansion should be slowing down due to the mutual gravitational attraction of all matter within the Universe. The precise nature of the dark energy that powers the acceleration is arguably the biggest puzzle that physics is facing today. Since the discovery, observations of the cosmic microwave background radiation have shown that dark energy makes up more than 70% of the total energy density of the Universe. The Hubble observations relied on a particular type of supernova explosion (known as Type Ia supernovae) to trace the expansion history of the Universe (figure 2), and thereby to place constraints on the properties of dark energy. There are two factors that make type Ia supernovae particularly useful in this regard. First, they are extremely bright, and therefore can be observed half way across cosmic time. Second, they are good standard candles — their luminosities are nearly constant — and therefore their distances can be determined quite accurately. Hubble's sharp vision has allowed astronomers to pinpoint distant supernovae in galaxies that are as far as nine billion light-years away, and to determine that dark energy was already present (though not dominant) even at that early stage, when gravity still had the upper hand and the expansion of the cosmos was decelerating.

Figure 2: Hubble spots distant supernovae in search of properties of dark energy. Image courtesy NASA.
All the observations to date are consistent with dark energy being the energy of empty space. Quantum mechanics, the theory that most accurately describes the sub-atomic world, says that the physical vacuum, far from being empty, is teeming with virtual particles that appear and disappear in split seconds. The energy density associated with the vacuum is constant, and characterised by an equation of state parameter w (the ratio of pressure to density), which, according to the theory, satisfies w = -1. Most of the current observational efforts are directed at determining whether w is indeed constant across cosmic time, and whether its value is equal to –1. However, even if the characteristics of dark energy will be found to be fully consistent with it being the energy of the vacuum, many open questions will remain. In particular, naive attempts to theoretically calculate the expected value of the vacuum energy density produce results that are more than 50 orders of magnitude higher than the observed value (see Plus article
Lambda marks the spot for more information). Consequently, a true understanding of dark energy will require a combination of observational efforts coupled with significant theoretical developments.

Galaxy formation and evolution
Figure 3: The heart of the Whirlpool Galaxy. Image courtesy NASA.
Everyone is familiar with the shapes of the galaxies that we see in the relatively local Universe. Galaxies such as the Milky Way and the Andromeda galaxy are disc galaxies: they are flattened like pancakes, and are characterised by a prominent spiral structure traced by young stars (figure 3). Other galaxies are elliptical: they are shaped like oval concentrations of relatively old stars. One of the key goals of astronomy is to understand how galaxies form and how they evolve. Astronomers using HST produced the deepest images of the Universe in optical light. These observations were dubbed the Hubble Deep Fields and the Hubble Ultra Deep Field (figure 4). The observations revealed that galaxies in the distant past were smaller in physical size, and that their shapes were much more irregular. These two properties are consistent with a scenario of hierarchical structure formation, in which smaller building blocks of galaxies collided and coalesced frequently in the early, dense Universe, to form the larger galaxies we observe today. Using HST's exquisite spatial resolution and photometric stability, astronomers were also able to observe in detail the stellar populations in the old halos of nearby galaxies, which allowed them to reconstruct how mass was assembled in these galaxies.

Figure 4: The Hubble Ultra Deep Field image reveals galaxies galore. Image courtesy NASA.
Finally, the deep-field observations yielded the history of the global rate of star formation in the cosmos. Even before the Hubble observations, astronomers knew that our Universe as a whole is past its peak in terms of the rate of birth of new stars. The peak occurred about 7 to 8 billion years ago. The Hubble Ultra Deep Field showed that when the Universe was less than one billion years old (the Universe today is 13.7 billion years old) the rate of cosmic star formation was lower than the peak value by about a factor of three, but already higher than the rate today, which is about a factor of ten lower than at the peak. In other words, once the Universe started forming stars, it did so furiously.
Supermassive black holes
Astrophysicists have long suspected that active galactic nuclei — the extremely bright cores of galaxies that show violent activity — and quasi-stellar objects (QSOs) create their extraordinarily high luminosities by accreting mass at a high rate onto a black hole that lies at their centre. The power emitted simply reflects the rate of release of gravitational potential energy. However, before HST it was virtually impossible to detect the host galaxies of QSOs, and it was extremely difficult to confirm the presence of a black hole, except in a couple of relatively nearby galaxies, and in our own Milky Way Galaxy. HST changed all that. First, it has unambiguously detected the host galaxies in a few relatively nearby QSOs. Second, by following the motions of individual stars (or of gas discs) around the centres of tens of galaxies, it has shown that essentially all the galaxies that have a central bulge of stars harbor a supermassive black hole at their centres (figure 5). The masses of these black holes range from a few millions to a few billions of solar masses. But in addition to the mere discovery of the black holes, HST provided two other significant pieces of information. First, high-resolution images of the hosts of QSOs revealed that many of them were interacting galaxies and the others were bright elliptical galaxies. This suggests that certain environments (such as the one resulting from an interaction) may be needed to funnel gas into the central regions to fuel the black holes.
Second and more important, the masses of the black holes were found to be tightly correlated with the masses of the smooth, spherical bulges of stars surrounding the galactic centres. This indicates that the black holes and their host galaxies do not evolve independently, but rather that their evolutions are intimately connected — massive black holes are apparently a generic feature of galaxy formation and evolution.

Extrasolar planets
Figure 6: A planet's telltale signature. Image courtesy NASA.
Until 1992, we did not know of a single planet outside our solar system. In 1992, the first so-called extrasolar planets were detected, but they did not orbit an ordinary star such as the Sun. Rather, they were found around a pulsar — an extremely compact object with a mass of about 1.4 solar masses, but a radius of only about 10km. The first planet around a Sun-like star was discovered in 1995. Since then, astronomers have discovered about 350 extrasolar planets. Most of these planets were discovered by ground-based telescopes. Still, HST has contributed a few unique observations to this field. First, Hubble focused on transiting planets — planets whose orbital planes are aligned with our line of sight, so that the planets periodically eclipse their host stars. When the planet passes in front of the star, it blocks some of the star's light. From the amount of dimming (typically 1-2%) the radius of the planet can be deduced (figure 6). But this is not all. Some of the starlight passes through the planet's atmosphere, where part of it is absorbed by various atoms. By concentrating on particular spectral lines, the presence and abundance of certain atoms and molecules can be determined (see Plus article Hunting for life in alien worlds for more on this technique). In this way, HST observations showed that the atmosphere of the planet around the star HD 209458 contains sodium, carbon, oxygen, and hydrogen. In another case, even water and methane were detected. These were the first determinations of the composition of atmospheres of extrasolar planets.
The Hubble Space Telescope against the Earth's horizon. Image courtesy NASA.
Most of the extrasolar planets were found around stars in the solar neighborhood. This still left open the question of whether the local fraction of stars hosting planets is typical of the Galaxy at large. To answer this question, HST observed about 180,000 stars in the crowded central bulge of our Galaxy, half-way across the Milky Way. These observations led to the discovery of 16 planet candidates, a tally consistent with the frequency of planets in the solar neighborhood, and they showed that the Galaxy is indeed teeming with billions of planets. Five of the planet candidates were found to whirl around their stars in less than one Earth day, and they were dubbed Ultra-Short-Period Planets.
Finally, HST produced the first visible-light snapshot of a planet orbiting another star. The planet, known as Fomalhaut b since it circles the bright southern star Fomalhaut, was resolved inside a large debris disc, somewhat similar to the Kuiper Belt in our own solar system. The planet's distance from its host star is about ten times the distance of the planet Saturn from the Sun.

Wednesday, December 17, 2008

Galileo's Discovery

Can you imagine making such a big discovery?

Galileo made an amazing contribution to the world of time, simply by not paying attention in church. The year was 1581 and Galileo was 17. He was standing in the Cathedral of Pisa watching the huge chandelier swinging back and forth from the ceiling of the cathedral. Galileo noticed that no matter how short or long the arc of the chandelier was, it took exactly the same amount of time to complete a full swing.
The chandelier gave Galileo the idea to create a
pendulum clock. While the clock would eventually run of energy, it would keep accurate time until the pendulum stopped. If the pendulum was set swinging again before it stopped, there would never be a loss in accuracy. Because of this, pendulums caught on and are still widely used today. Can you imagine making such a big discovery?






Tuesday, December 9, 2008

Following are the some of my collections of information based on mystery of the universe. I expect the same kind of information/questions/answers from you.

Mysteries of the universe:
1. If Heat can ONLY be transferred between objects by radiation, conduction and convection, then why a human body without space suit in a vacuum space gets cold/ frozen?
My comment: if there is no such medium in vacuum space to transfer heat and body is not emitting any radiation then how it is possible that body loses it heat without transferring it to any medium? It is mystery or something else….your comment please…..

2. Why our universe is expanding? As the distance among every massive object like satellite, planets, stars and galaxies are continuously increasing, even accelerating. The Moon is gradually moving away from the Earth and the tides are to blame. Is it really the reason, no one knows. Every year, the Moon moves a further 3.82cm from the Earth.
My comment: moon is shifting some inches from its orbit around the earth. But the question is why? Even If moon and earth both are retaining the same gravitational force continuously without any variation in it or losing it.

3. Why water boils in vacuum space before freezing?
My comment: there are many explanations given in several books that it happens due to the low or zero pressure around the water in the absence of atmospheric environment. Is it the only fact that applies on it? Or something is still unknown for our science? Your comment please….

4. Why the aircraft gets accelerated and get extra unexpected speed or extra ‘tug’ toward the sun that is not accounted for in the traditional theory? And why aircraft gets decelerated on outer-reason of our solar system?

  • The Pioneer spacecraft seems to be slowing down in a way which has yet to be explained.
  • Various spacecraft have experienced greater accelerations during slingshot maneuvers than expected.

5. Gravity is not, in itself, a force, but merely a consequence of universal expansion. Not only are galaxies moving apart, but stars, planets, atoms, the most fundamental particles, and the spaces between them are continuously expanding, which is what is 'pushing' the universe apart. No mass is being created in this expansion, and no changes in density of that mass are occurring.

6. Gravitational Lansing: A Mystery

7. “The conclusion of the theory of special relativity was that energy and mass are not separate things, but are, in fact, interchangeable” Sir Einstein discover the formula E=mc2, to calculate the total energy of the mass, and that seems absolutely right as per research. Now a question comes into my mind that:
‘Is there any evidence or any experiment done to come up with the practically proved logic that can explain how energy converts into mass?

8. Why a mass has gravity? There is no answer, Gravity is still a phenomena for current science, the following statement given by Newton put forwards the same question, and still unsolved:

  • Newton stated in “ThePhilosophiae Naturalis Principia Mathematica,”
    “I have not yet been able to discover the cause of these properties of gravity from phenomena and I frame no hypotheses... It is enough that gravity does really exist and acts according to the laws I have explained, and that it abundantly serves to account for all the motions of celestial bodies”

9. Gravitational mass is measured by comparing the force of gravity of an unknown mass to the force of gravity of a known mass. This is typically done with some sort of balance scale. The beauty of this method is that no matter where, or on what planet you are, the masses will always balance out because the gravitational acceleration on each object will be the same.
This does break down near super massive objects such as neutron stars due to the high gradient of the gravitational field around such objects.

Accepted and proved theory: but hard to believe for a common man.

1. Gravity is not a force; it is just a wrapage of space-time. In Einstein theory of general relativity, the effects of gravitation are ascribed to space-time curvature instead of a force. Your comment please….

Exceptions to the Einstein theory:
1. How the object which is very far from massive object knows or senses that space is wrapped around the massive object and it has to go there?

Amazing/Interesting Facts:
1. Why the conversion of energy into mass is not possible? (Einstein formula E=mc2 explains the conversion of mass into energy.)

2. Some neutron stars can spin up to 1000 times a second. More earthly objects such as CD-ROMs can spin up to 100 times a second whereas music CDs spin a meager 10 times a second.

3. If 10 kilograms of matter spontaneously turned into energy there would be enough energy to power a 100 Watt light bulb for 300 million years.

4. A supernova is the most energetic single event known in the Universe:
Material is exploded into space at a speed of about 10,000 kilometers per second and the energy emitted is 10 to the power of 44 Joules. Our galaxy contains about 100,000,000,000 stars and all these stars would have to shine for six months to produce this much energy.

5. The mass of the Earth increases every year because of the 3,000 tones of meteorite debris that hits its surface from space.

Incompatibility between two popular theories:

1. Several decades after the discovery of general relativity it was realized that general relativity is fundamentally incompatible with quantum mechanics. One can demonstrate that the structure of general relativity essentially follows inevitably from the quantum mechanics of interacting theoretical spin-2 mass less particles called gravitons. It means we are still missing some unknown but very important facts of gravitational force.

Comparison between two theories:
1. Gravity is in many ways a much better quantum field theory than the Standard Model. It indirectly means, in some situation, both the theories gives different result, hence both are somewhere incompatible with each other.

Successful theory that fails somewhere….

1. MOND, the original theory on which TeVeS is based, was already quite successful at explaining galactic dynamics. (even better, in some cases, than the dark matter paradigm), but it failed completely at explaining other observations—gravitational Lansing in particular,” explained Liguori. “For this reason, it couldn't be considered a real alternative to dark matter. (not successful on all parameters of gravity)

Why gravitational force is still an interesting phenomenon/subject for the world of science?
Many scientists DO NOT believe that gravity is a force at all, since they cannot detect any energy transfer or other mechanisms that act between separate objects under each other’s gravitational influence. Most scientists believe that for one body to act on another body from a distance requires an exchange of energy. While no such exchange has been identified, scientists have theorized and tried to find what they call gravity waves.
Einstein theorized that the total curvature of space time is split into two components: (1) the curvature of space and (2) time dilation. Einstein theorized that both components are responsible for gravity. According to Einstein, time is modified by mass so it runs slower near large bodies of mass and the dilation of space-time creates the illusion of gravity. Einstein explained that space-time is bent so it appears that an object is being moved by some "force of attraction" between the two objects of mass. Most scientists today accept that gravity is a phenomenon whereby large masses curve space and time within their vicinity. While there has been some experimental data that support parts of Einstein’s theory.
But some scientists cannot accept the concept that space-time is curved. In fact, much empirical evidence supports the contrary; thus, most scientists either force-fit everything into general relativity, while
a few scientists continue to grope for other theories that might explain the root cause of gravity.

If gravitation is a force of attraction, then what are the causes responsible for it?
  • How mass causes gravity?
  • What is the interchange vehicle that propagates gravity?
  • Why gravity appears to propagate instantaneously?
  • Why gravity appears to wrap or bend space-time but does not?

If gravitation is just a space- time curvature and not a force applied between two objects, as sir Einstein said, then:

  • Why and how physical existing mass can bend non-physically existing space-time?

Newton was puzzled that the root cause of gravity was beyond the reach of science. Newton was convinced “that there were causes hitherto unknown”. Newton said:
“That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it."

Great scientists: Newton and Einstein.
(Two theories with different logic, but almost same result……amazing.)
Einstein’s theory was used to explain how objects could affect each other at a distance, but it was not able to explain exactly how matter could curve space any more than the discovery of the Law of Universal Gravitation enabled Newton to explain his “force” of gravity. Einstein theorized the existence of gravity waves, which have never been discovered directly so far.
Crucial experiments that justified the adoption of General Relativity over Newtonian gravity were: the deflection of light rays by the Sun, and the precession of the orbit of Mercury, and gravitational red shift. Einstein’s theory of general relativity was able to explain those phenomenon better than Newton’s. General relativity was able to explain why Mercury's precession differs from Newtonian prediction. Einstein explained that since Mercury is the closest planet to the sun it moves faster than any other planet, and orbits the sun in space that is much more “curved” than the space near any of the other planets. This curved space affects the orbit of Mercury and Einstein’s calculations predict this behavior more accurately than Newton’s, but still with some error.
General Relativity also was more accurate that Newton’s in predicting the bending of light rays as they pass near the sun, because the Newtonian deflection of the ray corresponds only to the time dilation. Einstein’s formula also takes into account the relative curvature of space. Thus, Einstein’s calculated total deflection is twice as big as its Newtonian prediction. Experiments later validated that the observed deflection of light near the sun was more in line with Einstein’s predictions and within the observational error.
General relativity also explains the equivalence of gravitational, inertial, and centrifugal acceleration (the equivalency principle).

Nikola Tesla challenged Albert Einstein's theory of relativity:
(One of the scientist who had not accepted the logic ‘space-time curvature’)
Announcing he was working on a Dynamic theory of gravity, which he began in 1892. Tesla believed that gravity is the result of the field of force surrounding all matter. He stated:

“Only the existence of a field of force can account for the motions of the bodies as observed, and its assumption dispenses with space curvature. All literature on this subject is futile and destined to oblivion. So are all attempts to explain the workings of the universe without recognizing the existence of the ether and the indispensable function it plays in the phenomena ...”

Regarding Einstein’s theory of curved space, Tesla chided:

  • [The Dynamic theory of gravity] ... explains the causes and motions of heavenly bodies under it's influence so satisfactory that it will put to an end idle speculation and false conception, as that of curved space ...

On his 81st birthday on July 10, 1937 Tesla published a statement critiquing Albert Einstein's theory of relativity. The following is a portion of that statement:

  • ... Supposing that the bodies act upon the surrounding space causing curving of the same, it appears to my simple mind that the curved spaces must react on the bodies, and producing the opposite effects, straightening out the curves. Since action and reaction are coexistent, it follows that the supposed curvature of space is entirely impossible - But even if it existed it would not explain the motions of the bodies as observed. Only the existence of a field of force can account for the motions of the bodies as observed, and its assumption dispenses with space curvature. All literature on this subject is futile and destined to oblivion. So are all attempts to explain the workings of the universe without recognizing the existence of the ether and the indispensable function it plays in the phenomena...

While Tesla asserted that he had "worked out a dynamic theory of gravity" that he would soon give to the world, he revealed few details about his theory and died before publicizing any details.

A truth: Sir Einstein would have never ever thought in his life that his theory of relativity will achieve the highest level of success and achievements than any other theory.

  • “When Einstein introduced general relativity, it was rejected as contrary to known Newtonian physics, unsupportable and unverified. Now, general relativity is the accepted dogma of physics and appears as well entrenched as Newton’s theory was. But that was not the case in the 1920s”