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Ancient Black Hole Speeds Through Sun's Galactic Neighborhood, Devouring Companion Star

By Martha Matsamoto

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope have found an ancient black hole speeding through the Sun's Galactic neighborhood, devouring a small companion star as the pair travels in an eccentric orbit looping to the outer reaches of our Milky Way Galaxy. The scientists believe the black hole is the remnant of a massive star that lived out its brief life billions of years ago and later was gravitationally kicked from its home star cluster to wander the Galaxy with its companion.

Orbital Path (red line) of Black Hole and its Companion Through the Milky Way Galaxy Over the Past 230 Million Years. Yellow circle indicates the Sun's Current Position.

"This discovery is the first step toward filling in a missing chapter in the history of our Galaxy," said Felix Mirabel, an astrophysicist at the Institute for Astronomy and Space Physics of Argentina and French Atomic Energy Commission. "We believe that hundreds of thousands of very massive stars formed early in the history of our Galaxy, but this is the first black hole remnant of one of those huge primeval stars that we've found."

"This also is the first time that a black hole's motion through space has been measured," Mirabel added. A black hole is a dense concentration of mass with a gravitational pull so strong that not even light can escape it. The research is reported in the Sept. 13 issue of the scientific journal Nature.

The object is called XTE J1118+480 and was discovered by the Rossi X-Ray satellite on March 29, 2000. Later observations with optical and radio telescopes showed that it is about 6,000 light-years from Earth and that it is a "microquasar" in which material sucked by the black hole from its companion star forms a hot, spinning disk that spits out "jets" of subatomic particles that emit radio waves.

Most of the stars in our Milky Way Galaxy are within a thin disk, called the plane of the Galaxy. However, there also are globular clusters, each containing hundreds of thousands of the oldest stars in the Galaxy which orbit the Galaxy's center in paths that take them far from the Galaxy's plane. XTE J1118+480 orbits the Galaxy's center in a path similar to those of the globular clusters, moving at 145 kilometers per second (90 miles per second) relative to the Earth.

How did it get into such an orbit? "There are two possibilities: either it formed in the Galaxy's plane and was somehow kicked out of the plane or it formed in a globular cluster and was kicked out of the cluster," said Vivek Dhawan, an astronomer at the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico.

A massive star ends its life by exploding as a supernova, leaving either a neutron star or a black hole as a remnant. Some neutron stars show rapid motion, thought to result from a sideways "kick" during the supernova explosion. "This black hole has much more mass -- about seven times the mass of our Sun -- than any neutron star," said Dhawan. "To accelerate it to its present speed would require a kick from the supernova that we consider improbable," Dhawan added.

"We think it's more likely that it was gravitationally ejected from the globular cluster," Dhawan said. Simulations of the gravitational interactions in globular clusters have shown that the black holes resulting from the collapse of the most massive stars should eventually be ejected from the cluster.

"The star that preceded this black hole probably formed in a globular cluster even before our Galaxy's disk was formed," Mirabel said. "What we're doing here is the astronomical equivalent of archaeology, seeing traces of the intense burst of star formation that took place during an early stage of our Galaxy's development."

The black hole has consumed so much of its companion star that the inner layers of the smaller star -- only about one-third the mass of the Sun -- now are exposed. The scientists believe the black hole captured the companion before being ejected from the globular cluster, as if it were grabbing a snack for the road.

"Because this microquasar happened to be relatively close to the Earth, we were able to track its motion with the VLBA even though it's normally faint," said Mirabel. "Now, we want to find more of these ancient black holes. There must be hundreds of thousands swirling around in our Galaxy."

The astronomers used the VLBA to observe XTE J1118+480 in May and July of 2000, using the VLBA's great resolving power, or ability to see fine detail, to precisely measure the object's movement against the backdrop of more-distant celestial bodies. The VLBA observations were made at radio frequencies of 8.4 and 15.4 GHz.

In addition, they found that the object appears in optical images made for the Palomar Observatory Sky Survey (POSS) taken 43 years apart. The POSS images were digitized to allow for rapid search and analysis by the Space Telescope Science Institute. The data from both the radio and optical images allowed the astronomers to calculate the object's orbital path around the Galactic center.

"With the VLBA, we could start observing soon after this object was discovered and get extremely precise information on its position. Then, we were able to use the digitized data from the Palomar surveys to extend backward the time span of our information. This is a great example of applying multiple tools of modern astronomy -- telescopes covering different wavelengths and digital databases -- to a single problem," said Dhawan.

Stay Curious.

Michael Graham Richard

Near Earth Objects and Asteroids: Are We Whistling in the Dark?

The universe is mostly empty, but not quite. Asteroids, also called minor planets or planetoids, float around and can potentially be dangerous for the Earth. Just looking at a map of the asteroids in the solar system should be enough to convince most people that we are not as alone in our corner of space as we sometimes might think.

A study on asteroids from 2002 said:

Asteroids in our Solar System may be more numerous than previously thought, according to the first systematic search for these objects performed in the infrared, with ESA’s Infrared Space Observatory, ISO. The ISO Deep Asteroid Search indicates that there are between 1.1 million and 1.9 million ’space rocks’ larger than 1 kilometre in diameter in the so-called ‘main asteroid belt’, about twice as many as previously believed.

Don’t panic, there’s this reassuring sentence:

However, astronomers think it is premature to revise current assessments of the risk of the Earth being hit by an asteroid.

But what comes right after it reveals how problematic things can be:

Despite being in our own Solar System, asteroids can be more difficult to study than very distant galaxies. With sizes of up to one thousand kilometres in diameter, the brightness of these rocky objects may vary considerably in just a few minutes. They move very quickly with respect to the stars - they have been dubbed ‘vermin of the sky‘ because they often appear as trails on long exposure images. This elusiveness explains why their actual number and size distribution remains uncertain. Most of the almost 40,000 asteroids catalogued so far (1) orbit the Sun forming the ‘main asteroid belt’, between Mars and Jupiter, too far to pose any threat to Earth. However, space-watchers do keep a closer eye on another category of asteroids, the ‘Near Earth Asteroids’ or ‘NEAs’, which are those whose orbits cross, or are likely to cross, that of our planet.

Though the asteroid belt itself, being relatively far from Earth, is not directly a problem (the inner edge of it is farther than Mars’ orbit, which is itself at half the distance between the Earth and the Sun, or 0.5 Astronomical Unit), it is important to better understand it because that’s where most of the “Near Earth Asteroids” (NEAs) or “Near Earth Objects” (NEOs) come from, and those share the same characteristics as belt asteroids (elusive “vermin of the sky”).

most NEA are believed to be former main belt asteroids. In the main belt there are four ’special’ regions where Jupiter’s gravitational influence is especially disruptive; originally, most asteroids currently known as NEA suffered collisions which resulted in them ending up in one of those four key regions, and because of Jupiter’s gravitational influence their orbits quickly evolved into Earth-crossing orbits. Therefore, by studying the asteroids near these so-called ’source regions’ in the main belt astronomers can learn about NEA. About 500 NEAs have been found so far*, and none of them pose any threat to Earth in this century.

* The study above was published in 2002. According to this NASA page, the number in 2002 was 523, but in 2007 (so far, up to April) it is up to 707 known “large” (one kilometer of diameter or larger) Near Earth Asteroids (NEAs).

The total number of known NEAs was 2165 at the end of 2002 and 4647 in April 2007. Here is a graph of the data from 1980 to November 2006:

Another interesting page on the NASA site is the NEO Earth Close Approaches page. It shows the recent and upcoming “close approaches” with the date, the miss distance (calculated in Astronomical Units, one being 149,597,870.691 kilometers, and “lunar distances”, one being 384,000 kilometers), the estimated diameter of the object, and the velocity of the NEO relative to the Earth’s (in kilometer per second).

The closest recent “close approach” detected was an object with an estimated diameter of 29 to 65 meters. It flew by the Earth at 9.32 kilometers per second on April 2, 2007. It missed by 5.3 lunar distances, or about 2.03 million kilometers.

The closest “upcoming approach” is for a relatively small object about 30 to 67 meters in diameter (about the size of a big house, think McMansion) that should pass by the Earth at about 2.1 lunar distances (806,400 kilometers) on April 16, 2007, moving at about 16.93 kilometers per second. Mark your calendar.

The Wikipedia article on meteorites says:

Most meteoroids disintegrate when entering the Earth’s atmosphere. However an estimated 500 meteorites ranging in size from marbles to basketballs or larger do reach the surface each year; only 5 or 6 of these are typically recovered and made known to scientists.

This NASA site says:

Millions of meteors occur in the earth’s atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles (65 and 120 kilometers) above the earth. They disintegrate at altitudes of 30 to 60 miles (50 to 95 kilometers). […]

The size of meteorites varies greatly. Most of them are relatively small. The largest meteorite ever found weighs about 66 short tons (60 metric tons). It fell at Hoba West, a farm near Grootfontein, Namibia. However, much larger bodies, such as asteroids and comets, can also strike the earth and become meteorites.

So an object the size of a large house would definitely not fall into the category of normal meteorites, and it would reach the Earth without completely disintegrating in the upper atmosphere (unless it is made of ice or something similar, I suppose).

What are the probabilities (as far as we can currently tell) that a NEO of “large” size could impact the Earth in the near future?

This page on the NASA site shows “impact risks”:

[JPL] Sentry is a highly automated collision monitoring system that continually scans the most current asteroid catalog for possibilities of future impact with Earth over the next 100 years. Whenever a potential impact is detected it will be analyzed and the results immediately published here, except in unusual cases where an IAU Technical Review is underway.

Right now, the whole page is a very relaxing sight. It is color-coded, with blue for objects that have an “estimated diameter 50 meters or less” and are “not likely to cause significant damage in the event of an impact, although impact damage does depend heavily upon the specific (and usually unknown) physical properties of the object in question” (so it depends), and white means:

The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage.

You can see the other colors on the Torino scale here.

Here is what they say about objects that would be categorized in the Red Zone:

Thankfully, the probabilities of a serious impact are very low, but we also have to remember that reality doesn’t care much about our statistics; if we are using erroneous data to make our predictions, it is very possible that our current level of risk is higher than we think. There is also always the fact that some people do win the lottery despite the odds, and that if humanity is planning on sticking around for a long time, we’ll need to face the problem eventually — better sooner rather than later.

I am not in a position to precisely tell if our current defense system is adequate, but from the little I know, it doesn’t seem to be. I don’t think that we are allocating enough resources to track as many Near Earth Objects as our technology allows us to, but most importantly, we don’t have a system that would allow us to do something if we detected a threatening object.

The Lifeboat Foundation has a page about Asteroid Impacts and the necessity of creating an “Asteroid Shield”:

If we don’t do something, sooner or later Earth will be hit by an asteroid large enough to kill all or most of us. That includes the plants and animals, not just people. Maybe this won’t happen for millions of years. Maybe in 15 minutes. We don’t know. For example, on 23 March 1989 asteroid 1989FC with the potential impact energy of over 1,000 megatons (roughly the equivalent a thousand of the most powerful nuclear bombs) missed Earth by about six hours [1]. We first saw this fellow after closest approach. If 1989FC had come in six hours later most of us would have been killed with zero warning.

The method they suggest is very elegant:

Picture credit: Dan Durda

The goal is to first detect the asteroid and then to alter its orbit [9]. If you attempt to destroy an asteroid as they often do in Hollywood movies, you will likely change the situation from a single impact situation to a many impact situation. […]

We support the proposal by the B612 Foundation to significantly alter the orbit of an asteroid in a controlled manner by 2015. They propose use of the gravity deflection approach, where you station a spacecraft a short distance from the asteroid, and use the gravitational attraction between spacecraft and asteroid to pull the asteroid off course.

This method would be less likely to break up an asteroid than alternative methods since there would be no physical contact with the asteroid. You do not want the asteroid to break into multiple pieces as you will then have multiple problems instead of one problem [8]. Also note that a large asteroid could be blown apart by a nuclear device detonated in its core only to have gravity draw the asteroid back together, essentially nullifying the effect of the explosion.

On the detection front, one interesting (but still at a very early stage) project is Orbit@Home, a distributed computing project running on the Berkeley Open Infrastructure for Network Computing. The project is currently active and will calculate the orbit of as many NEOs as possible and report, as fast as possible, the result so that - if need be - we can act.

The lead developer of the project answers some questions about it in this discussion forum thread:

[T]he data relative to the asteroids is already collected by the Minor Planet Center. Every observer is asked to send his observations there, and then MPC processes them, and publishes the Minor Planet Electronic Circulars, or MPECs. The latest MPECs are available here. So as a beginning, orbit@home will monitor these files. Every time a new MPEC is published, the data is collected and processed by [orbit@home], creating [work units], waiting for results, and then updating the local database. Orbit@home doesn’t need to recruit astronomers, or have any particular connection with observatories. All the data available will be processed by o@h, without limits on country or team. Backyard astronomers are welcome, but before they should go trough the process of getting an MPC code, that also certifies the quality of the data (see MPC website).

Orbit@Home has been active since February 26, 2007, when they have announced that they finally got enough funding to allow them to release a public beta and have “new work units generated on a daily basis, and a graphical screen saver. You can sign up for the project and have you BOINC client on standby (you can join more than on project, so in the meantime you can crunch other kinds of scientific data).

Well, that’s it for now. I’ve learned a lot writing this post, and I hope that you had fun reading it.

Stay curious.

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Sun's Direct Role in Global Warming May Be Underestimated, Duke University Physicists Report

Study does not discount the suspected contributions of 'greenhouse gases' in elevating surface temperatures

Durham, N.C. -- At least 10 to 30 percent of global warming measured during the past two decades may be due to increased solar output rather than factors such as increased heat-absorbing carbon dioxide gas released by various human activities, two Duke University physicists report.

The physicists said that their findings indicate that climate models of global warming need to be corrected for the effects of changes in solar activity. However, they emphasized that their findings do not argue against the basic theory that significant global warming is occurring because of carbon dioxide and other “greenhouse” gases.

Nicola Scafetta, an associate research scientistworking at Duke's physics department, and Bruce West, a Duke adjunct physics professor, published their findings online Sept. 28, 2005, in the research journal Geophysical Research Letters.

West is also chief scientist in the mathematical and information sciences directorate of the Army Research Office in Research Triangle Park.

Scafetta's and West's study follows a Columbia University researcher's report of previous errors in the interpretation of data on solar brightnesscollected by sun-observing satellites.

The Duke physicists also introduce new statistical methods that they assert more accurately describe the atmosphere's delayed response to solar heating. In addition, these new methods filter out temperature-changing effects not tied to global warming, they write in their paper.

According to Scafetta, records of sunspot activity suggest that solar output has been rising slightly for about 100 years. However, only measurements of what is known as total solar irradiance gathered by satellites orbiting since 1978 are considered scientifically reliable, he said.

But observations over those years were flawed by the space shuttle Challenger disaster, which prevented the launching of a new solar output detecting satellite called ACRIM 2 to replace a previous one called ACRIM 1.

That resulted in a two-year data gap that scientists had to rely on other satellites to try to bridge. "But those data were not as precise as those from ACRIM 1 and ACRIM 2,” Scafetta said in an interview.

Nevertheless, several research groups used the combined satellite data to conclude that that there was no increased heating from the Sun to contribute to the global surface warming observed between 1980 and 2002, the authors wrote in their paper.

Lacking a standardized, uninterrupted data stream measuring any rising solar influence, those groups thus surmised that all global temperature increases measured during those years had to be caused by solar heat-trapping "greenhouse" gases such as carbon dioxide, introduced into Earth's atmosphere by human activities, their paper added.

But a 2003 study by a group headed by Columbia's Richard Willson, principal investigator of the ACRIM experiments, challenged the previous satellite interpretations of solar output. Willson and his colleagues concluded, rather that their analysis revealed a significant upward trend in average solar luminosity during the period.

Using the Columbia findings as the starting point for their study, Scafetta and West then statistically analyzed how Earth's atmosphere would respond to slightly stronger solar heating. Importantly, they used an analytical method that could detect the subtle, complex relationships between solar output and terrestrial temperature patterns.

The Duke analyses examined solar changes over a period twice as long -- 22 versus 11years -- as was previously covered by another group employinga different statistical approach.

"The problem is that Earth's atmosphere is not in thermodynamic equilibrium with the sun," Scafetta said. "The longer the time period the stronger the effect will be on the atmosphere, because it takes time to adapt."

Using a longer 22 year interval also allowed the Duke physicists to filter out shorter range effects that can influence surface temperatures but are not related to global warming, their paper said. Examples include volcanic eruptions, which can temporarily cool the climate, and ocean current changes such as el Nino that affect global weather patterns.

Applying their analytical method to the solar output estimates by the Columbia group, Scafetta's and West's paper concludes that "the sun may have minimally contributed about 10 to 30 percent of the 1980-2002 global surface warming."

This study does not discount that human-linked greenhouse gases contribute to global warming, they stressed. "Those gases would still give a contribution, but not so strong as was thought," Scafetta said.

"We don't know what the Sun will do in the future," Scafetta added. "For now, if our analysis is correct, I think it is important to correct the climate models so that they include reliable sensitivity to solar activity.

"Once that is done, then it will be possible to better understand what has happened during the past hundred years."
 

© 2008 Office of News & Communications Duke University
615 Chapel Drive, Box 90563, Durham, NC 27708-0563

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NASA News Release

US budget proposal offers hope for climate research

Three of five climate-monitoring instruments cut from the future NPOESS network of satellites will be launched on other missions (Image: NPOESS)

In a rare bit of budgetary good news for climate and Earth-science research, the White House's proposed budget for fiscal year 2009 includes money for new satellite missions.

The proposal would give NASA a $103 million down payment on new missions given top priority for the coming decade in a 2007 survey by the US National Research Council. And the National Oceanic and Atmospheric Administration (NOAA) would get $74 million to help pay for instruments needed to extend three key sets of climate data.

The NASA project is aimed at new capabilities to replace a shrinking fleet of US instruments. The decadal survey warns that these instruments, which numbered about 120 at their peak in 2005, could drop by more than a third by 2010.

To stem the tide of these losses, NASA would receive $910 million through 2013 to develop at least three new missions recommended by the panel, according to forecasts in the proposed budget.

These include one called ICES at II, designed to measure changes in the height of ice sheets and planned for launch in 2015, and another called SMAP, which would launch in 2012 to measure soil moisture and freeze-thaw cycles. But the proposed amount is well short of the $1.5 billion the panel had recommended for their top priorities from 2010 to 2013.

Massive overruns

The NOAA funding is intended to rescue instruments threatened with cancellation by massive overruns on a joint military-civilian programme called the National Polar-Orbiting Operational Environmental Satellite System (NPOESS).

In mid-2006, projected costs of the six-satellite NPOESS system, in planning since 1994, crossed a threshold that forced major cutbacks. Pentagon managers made weather forecasting their top priority and cut the fleet to four satellites, with the first to fly in 2013.

Among the casualties were five key climate instruments, three of which are restored in the 2009 budget. The cuts had originally removed the ability to profile the vertical distribution of ozone – which, at high altitudes, protects the planet from the Sun's harmful ultraviolet rays.

Continuous record

But in April 2007, NOAA restored that capability and announced plans to launch the whole Ozone Mapping and Profiler Suite (OMPS-Limb) instrument in 2010 on another satellite called NPP (NPOESS Preparatory Project). Continued funding is included in NOAA's 2009 budget proposal.

CERES, a sensor to measure the Earth's radiation budget, had already been finished when it was bumped from NPOESS. Researchers consider it critical to assure the continuity of data with another CERES instrument launched on the Aqua satellite in 2002, so NOAA has already booked space for the completed instrument on NPP. It also plans to build another CERES for launch on the first NPOESS mission in 2013.

NOAA is shifting some money from the 2008 budget to a third cancelled instrument for measuring total solar irradiance – the amount of solar energy that passes through a 1-square-metre patch outside the Earth's atmosphere every second. In 2009, it will continue that development and try to find a satellite to carry it. Solar irradiance measurements are particularly tricky because they need to be accurate to about 1 part in 1000, and with a data set going back to 1979, many researchers are particularly keen on maintaining a constant stream of data.

Despite the good news, the NRC's 2007 decadal survey also urged the restoration of the other two instruments that had been cut from NPOESS, intended to measure sea-surface temperatures and wind directions over the oceans. Those instruments are not mentioned in the White House's 2009 budget request.

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10 Great Scientific Discoveries

By David Zimmerman

Science Editor

(Technological breakthroughs get big press because they can give us new tools and toys. We feel technology's impact directly: wheels and gears, zippers and microchips--the list is endless. But where would technology be without scientific discovery? Nowhere, I say. Technology marches on a highway laid down by those absent-minded geeks who merely figure out what's true. So what are the ten greatest scientific discoveries of all time? Here's my list. Forgive me for leaving out out Copernicus, Galleo, and Keppler. In a list of 15 or 20 they would have been included. Ed.)

1.      The Pythagorean Theorem

It's a staple of high school geometry: in every right triangle, a² + b² = c², where a and b stand for the two short sides and c for the long. The first to prove this was (probably) the Greek philosopher Pythagoras

 

in the 6th century bc. But it's not the theorem per se that matters; it's the bigger idea it reflected. Pythagoras taught that numbers were the real reality, that the core of the physical world was mathematical. That's why he went around telling everyone, 'Here's a pure idea that is true of every actual object of a certain shape.' Coupling physics to mathematics proved to be one of the most fruitful marriages of all time. Even now we regard a scientific theory as really reliable if it can be proven mathematically.

2.      The Existence of Microorganisms. In the late 1600s, when microscopes were new, Dutch lens maker Antoni van Leeuwenhoek scraped some plaque off his own teeth and looked at it through a microscope. Gasp! It was crawling with "animalcules."

In fact, tiny creatures invisible to the naked eye abounded everywhere, he found. Less than two centuries later, knowledge of this invisible universe enabled Louis Pasteur to construct his "germ theory of disease, "which in turn enabled doctors to conquer a whole host of diseases: typhoid, typhus, polio, diphtheria, tetanus, smallpox tuberculosis, anthrax--the list goes on. The leading cause of death changed after that from infectious disease to heart disease, cancer, and "old age."

3.      The Three Laws of Motion

Pythagoras would have been so proud of Isaac Newton! More than any scientist in history, this 18th-century Englishman succeeded in reducing physics to

mathematics. Newton came up with three laws to explain the motion of all objects in the universe, from runaway trains to orbiting planets. (He also invented differential calculus, explained gravity, and discovered the spectrum--not bad for one lifetime.)

4.      The Structure of Matter

In 1789, five years before he was beheaded by a guillotine, French chemist Antoine Lavoisier published a list of "elements"--substances that he said could not be

broken down further by any chemical process. His list was incomplete and contained mistakes, but he was onto something. Building on his work, chemists developed our modern view that all matter can be broken down into just 109 elements, that all elements are made of atoms, and that all atoms are made of just three types of particles--protons, neutrons, and electrons.

5.      The circulation of blood. Each person has a fixed amount of blood circulating throughout his or her system in one fixed direction. This fact, first discovered in the 12th century by an Arab doctor named Ibn al-Nafis, was rediscovered--for good,
 

this time--by the 17th-century English doctor William Harvey. Harvey's work opened the floodgates to research a full understanding of the physiology of living bodies, human and animal.

6.      Electrical currents. Ancient people knew about static electricity--rub something and it gives off a spark. They knew about lightning bolts--get struck by one and you're dead meat. But not till 19th-century scientists (such as Alessandro Volta) got

electricity to flow did people become aware of this as a distinct force. Today, electricity powers everything from light bulbs to computers, of course. But the discovery of electricity is bigger than its practical applications. Once scientists knew about this force, they couldn't stop wonderin