Журавлева Сборник текстов для подготовки аспирантов-физиков 2011

"That is the wrong direction, and it is really hard to see how that could happen," Unruh says.

The direction of emission is "a major point of ongoing discussion," Faccio says, noting that the position of the photon detector was chosen to minimize contamination from the laser. "I sort of prefer to think of it the other way around—we have a spectrum of photons that agrees exactly with theoretical predictions for the event horizon. Now we need to properly understand in detail why they're generated." Ted Jucobson of the University of Maryland remains on the fence as well, noting that although the emitted photons have some attributes that would be expected from an analogue of Hawking radiation, other predicted features have yet to be confirmed. For instance, the experiment performed by Faccio's group does not allow the researchers to verify that the photons appear in quantum-mechanically correlated pairs at the event horizon.

"In our big piece of glass we have no way of saying where the other photon will end up," Faccio notes. But Leonhardt's group, which is investigating the same phenomenon in optical fibers rather than blocks of glass, might be able to detect both photons from a separated pair and show their common origin. "Once he does that, I think it will close all the discussions," Faccio says. "That will be an undeniable proof that this idea is correct."

Vocabulary

infuse - вливать (о жидкости);) Syn: implant; привносить; незаметно внушать Syn: introduce insinuate; вдохновлять, воодушевлять ripple - зыбь, рябь, небольшая волна (на поверхности воды) Syn: swell, riffle, wavelet; волна на поверхности жидкости, противодействующая сила для которой обеспечивается в большей степени по-

верхностным натяжением, чем силой тяжести seek - sought - искать

trickling out – просачиваться, течь тонкой струйкой

transient - кратковременный, мимолётный, недолговечный, преходящий, скоротечный

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fused - расплавленный; perturb - возмущать, нарушать

trait - характерная черта, особенность contamination - загрязнение; заражение

mundane - земной, мирской, светский Syn: secular , worldly;

обычный, приземлённый; космический

sort of - отчасти, вроде, как бы, в известной мере

undeniable - неоспоримый, несомненный, неопровержимый, явный

Find out

What two practical demonstrations of Stephen Hawking prediction made in 1974 are given in the article?

What is event horizon?

Why is it impossible even for light to escape from black hole?

Imagine you’re telling your friend about a black hole. What facts from the text would you mention?

Render the text using the facts you’ve chosen.

Unit 6

You may use this text to practice your written or oral translation

The Biggest Bang Theory: Astronomers Confirm a New Type of

Supernova

A new type of supernova is forcing astronomers to rethink the lives of the biggest stars

By Michael Moyer, September 30, 2010

When our sun comes to its ending in five billion years or so, it will fade into a quiescent white dwarf. Bigger stars go out with a bang - those with more than 10 times the mass of our sun collapse with enough

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vigor to spark a supernova, one of the most energetic events in the universe. For decades astronomers have suspected the existence of a type of stellar explosion that is bigger still - a “pair-instability” supernova, with 100 times more energy than an ordinary supernova. In the past year two teams of astronomers have finally found it, redrawing in a stroke the limit of how big things can be in this universe of ours. All stars balance gravity with pressure. As light elements such as hydrogen fuse in a star’s core, the reactions generate photons that press outward, counteracting the pull of gravity. In larger stars, pressure at the core is high enough to fuse heavier elements such as oxygen and carbon, creating more photons. But in stars bigger than 100 solar masses or so, there’s a hitch. When oxygen ions begin to fuse with one another, the reaction releases photons that are so energetic, they spontaneously trans mute into electron-positron pairs. With no photons, there’s no outward pres- sure—and the star begins to collapse. One of two things can happen next. The collapse can create even more pressure, reigniting enough oxygen to create a burst of energy. This burst is enough to toss off the outer layers of the star but not enough to create a full supernova. The cycle can repeat itself in pulses—astronomers call this case a “pulsational” pair-instability supernova—until the star loses enough mass to end its life in an ordinary supernova. A team led by the California Institute of Technology’s Robert M. Quimby announced it had identified one of these and has submitted a paper for publication. If the star is really big—and here we’re talking more than 130 solar masses—the collapse happens so fast and gathers so much inertia that even fusing oxygen can’t stop it. So much energy develops in such a little space that eventually the whole thing blows up, leaving no remnant behind. This is “the real deal, the big stuff,” says Avishay Gal-Yam, an astronomer at the Weizmann Institute of Science in Rehovot, Israel, whose team claims in a recent paper in Nature to have discovered the first full-fledged pairinstability supernova. Before the findings, most astronomers had argued that gigantic stars in nearby galaxies slough off much of their mass before dying out, precluding a pair-instability supernova. These ideas are being reconsidered, now that these biggest of explosions have announced themselves in spectacular fashion.

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Unit 7

Warming up activities

Do you think life is possible on other planets or we are alone in the universe?

What have you heard about ecoplanets? Do you know methods of defining them?

How far are they from our Earth?

Planet Hunters Discover a World That Could Harbor Life

A newfound "super-Earth" just 20 light-years away appears to reside in the habitable zone of its host star

By John Matson September 30, 2010

A LAND NOT SO FAR AWAY: Twenty light-years away, astronomers have located what might be the most hospitable world yet discovered outside our solar system. This artist's conception depicts the Gliese 581 planetary system, with the potentially habitable Gliese 581g in the foreground. After more than a decade of telescopic monitoring, astronomers have added two newfound worlds to a nearby planetary system already known to harbor four other planets, and one of the new discoveries looks to be the kind of place where life might be able to take hold.

"Since the beginning of this hunt we've tried to find planets at about the size of the Earth with temperatures so that water can exist," said one of the researchers, Steven Vogt of the University of California, Santa Cruz, in a Webcast press briefing on September 29. "This is the first exoplanet that really has the right conditions for water to exist in liquid form on its surface." Vogt and his colleagues are set to publish their findings in a future issue of the Astrophysical Journal. By monitoring a small, nearby star for 11 years with one of the 10-meter Keck telescopes in Hawaii and combining the data with 4.3 years of similar observations published by another team, Vogt and his co-authors

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found two orbiting planets, with respective masses of at least 3.1 times and seven times the mass of Earth. Both qualify as quite small in the field of known exoplanets, in which most of the hundreds of worlds that have been discovered are giants larger than Jupiter. The planetary system, which encircles the red dwarf star Gliese 581 only 20 light-years away, now ranks among the largest known. (In August it was announced that another planetary system boasts at least five, and possibly seven, worlds.)

Of the four previously known planets orbiting the diminutive star, two bracket what astrobiologists call the habitable zone, or the "Goldilocks zone"—the region of space surrounding a star that is neither too hot nor too cold for liquid water and just possibly life. The smaller of the two new worlds, Gliese 581g, orbits right between those two planets, placing it more squarely in the star's habitable zone. Nevertheless, Earthlings would not mistake Gliese 581g for their home planet—in addition to its so-called super-Earth dimensions, it orbits a star far smaller and dimmer than the sun, and its average surface temperatures would vary dramatically, from well below freezing on its night side to scorching hot on the day side.

But somewhere between those temperature extremes, which Vogt estimated might range from –35 to 70 degrees Celsius, would exist stable climatic bands, which Vogt called "eco-longitudes," within which liquid water might persist. Because the planet is probably tidally locked, showing only one hemisphere to its star just as the moon does to Earth, the temperate band between permanent daylight and permanent night might afford life a toehold. "There is a continuum of temperatures in between that are stable," Vogt said. "You just have to move around on the surface."

The actual surface temperatures of Gliese 581g depend on a number of factors that are currently unknown - such as the planet's reflectivity and the strength of any greenhouse effect it might have. "We can't say anything for sure about its atmosphere or about water," study co-author Paul Butler of the Carnegie Institution of Washington said during the Webcast. But what is known about the planet qualifies it as at least potentially habitable. "Its mass would be sufficient to hold a nice, strong

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atmosphere like Earth," Butler said, "and there would be places on the surface that would be sufficient for water." The radial-velocity, or "wobble," technique used to identify the new planets relies on tracking Doppler shifts in the host star's light as orbiting planets tug on the star, drawing it nearer to and then farther from Earth. The radial-velocity method has been an extraordinarily productive technique since it was used to identify the first exoplanet orbiting a sunlike star in 1995, but it yields a partial portrait of an exoplanet - revealing only lower bounds for planetary masses, for instance, which can produce ambiguities about whether a planet is rocky, like Earth, or gaseous, like Jupiter, or whether it is an even larger object such as a brown dwarf. In the case of Gliese 581g, it appears that the stability of the planetary system would be compromised if the planet were much more than 4.3 times as massive as Earth.

To get a better picture of the newfound world, astronomers would need a complementary observation, such as watching a partial eclipse (known as a transit) as the planet passes in front of its star, or making a precision measurement of the star's side-to-side motion in the sky. With a planetary transit, researchers can even identify constituents of a planet’s atmosphere that might indicate the presence of biological organisms there. But Gliese 581g does not appear properly aligned to transit its star from Earth's vantage point. And instruments for astrometry, which measure stellar positions on the sky, are not yet up to the task. "We're hopeful that continuing advances in astrometry will lead to a confirmation of this discovery and lead to a more precise mass estimate for this planet," Butler said.

Even so, the new paper presents "a marvelously intriguing result," says Geoff Marcy, a University of California, Berkeley, astronomy professor who has collaborated with Vogt and Butler on numerous planet discoveries in the past but was not involved in the new study. Gliese 581g, Marcy says, "is certainly extraordinary for its low mass and for being in the habitable zone."

"It's a very exciting step forward," says David Charbonneau, an astronomer at the Harvard–Smithsonian Center for Astrophysics, who adds that the group collected some "really beautiful data" over the years.

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Teasing out the subtle signature of small planets in radial-velocity data takes a wealth of observations, especially when the signal is dominated by larger planets in the system, and others are sure to investigate whether the signature of Gliese 581g is real. "There are competing groups that will do their best to see if they can confirm the signal or not," Charbonneau says. "They're probably running those analyses right now, because they learned about this five minutes ago."

Even if the planet proves out, the question of whether Gliese 581g actually hosts any biological activity will remain open. "Any discussion of life at this point is of course speculative," Butler cautioned. "That being said, on Earth, anywhere you find liquid water you find life in abundance."

Vocabulary

diminutive - уменьшительный, диминутивный Ant: augmentative;

маленький, крохотный, миниатюрный bracket - группа, класс, разряд, категория squarely - прямо 2) лицом к лицу

dim - тусклый, неяркий; слабый (о светящихся объектах) scorching - палящий, жаркий, знойный; обжигающий; сжигаю-

щий

tidal - приливной; связанный с приливно-отливным движением океана

toehold - точка опоры ; поддержка, зацепка

wobble - качание; колебание; биение; неустойчивое движение; качаться, колебаться

tug - рывок, тянущее усилие

ambiguity - двузначность, многозначность, неоднозначность, неопределённость

aligned - выпрямленный, выровненный, находящийся на одной линии

vantage - преимущество 2) превосходство в соревновании; выгодное положение; выигрышная позиция

Teasing out – вытягивать, определять

Subtle - неуловимый, тонкий; едва различимый abundance – изобилие; избыток

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Think and say a few words about:

-history of ecoplanet search

-ways of defining them

-environment they could have

-possibility of existing life there

Organize a discussion in your group. Following phrases will help you:

-in my opinion

-first of all

-in general

-in the end

-my aim is

-consequently

-as stated

-as have already been mentioned

-to my mind

-as mentioned above

-generally speaking

While making a presentation you should keep in mind the following points

Good communicators:

-listen to people and take in what is said

-maintain eye contact and have a relaxed body language

-seldom interrupt and stop people talking

-if they want to clarify something the wait for a suitable opportuni-

ty

-good at given information

-do not confuse their listeners

-make their point clearly

-avoid technical terms, abbreviations or jargon

-give easy to understand examples

-not lose sight of their main message

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Unit 8

You may use this text to practice your written or oral translation

Planet Survived Brush with Red Giant

Will the sun destroy Earth? Astronomers come closer to an answer.

By ОК Minkel September 12, 2007

CLOSE CALL: A newly discovered planet survived the red giant phase of its parent star, as depicted in this artist's conception. Astronomers have detected the first planet orbiting a star that has passed through the red giant phase, the massive bloating that befalls sun-like stars when their nuclear fuel begins to run out. The so-called exoplanet likely survived a close brush with its star, V391 Pegasi, despite once orbiting at roughly the same distance that lies between the sun and Earth, according to a study published in Nature. Researchers believe that when the sun goes red giant in five billion or six billion years, it will swallow Mercury and Venus, but they are unsure about Earth's future. Will solar wind vaporize our home planet? Could it tumble into the sun? The discovery does not reveal Earth’s destiny, but it suggests that further observations of similar star systems could lead to models that can, says astrophysicist Roberto Silvotti of the Capodimonte Observatory in Naples, Italy. When a medium-size star like the sun burns most of its nuclear fuel, it collapses and then balloons into a cooler red giant. Eventually much of this new outer envelope blows away, but in about 2 percent of cases, stars lose nearly their entire envelope. Researchers believe V391 Pegasi is such a star, called a B subdwarf, that shrunk from about 0.9 solar mass during its youth to 0.5 solar mass today. It is also one of a handful of B subdwarfs known to pulsate in brightness every few minutes. Silvotti and his colleagues chanced upon the new planet, V391 Pegasi b, during a seven-year study of these pulsations. Looking for clues to the star's structure, they noticed a regular variation in the timing of the pulses, which implied the presence of a planet at least 3.2 times the mass of Jupiter tugging the star back and forth. The variations indi-

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cate that V391 Pegasi b orbits at about 160 million miles, or 1.7 times Earth's distance from the sun, called an astronomical unit (AU). The most likely scenario, the researchers say, is that the planet once orbited about one AU from V391 Pegasi, which closed the gap to 0.3 AU during its red giant phase and finally lost its outer mass, allowing the planet to migrate farther away. The finding "does suggest at least some of the planets in our solar system will survive through the red giant phase," says astrophysicist Matt Burleigh of the University of Leicester in England. He says it also boosts the odds of discovering planets around white dwarfs, the typical remnants of stars like our sun that have passed through a second, bigger red giant phase. Such planets could finally spell out Earth's fate. "Until you start finding planets around these stars," Burleigh says, "theoreticians can only make guesses."

Supplementary Reading

How Time Flies: Ultraprecise Clock Rates Vary with Tiny Differences in Speed and Elevation

Newly developed optical clocks are so precise that they register the passage of time differently at elevations of just a few dozen centimeters or velocities of a few meters per second

By John Matson September 23, 2010

If you have ever found yourself cursing a noisy upstairs neighbor, take solace in the fact that he or she is aging faster than you are.

Albert Einstein's theory of general relativity predicts that clocks at different gravitational potentials will tick at different rates - a clock at higher elevation will tick faster than will a clock closer to Earth's center. In other words, time passes more quickly in your neighbor's upstairs apartment than it does in your apartment.

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