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Transcript
1
Calendar of Events
PUBLIC OBSERVING
Prairie Park Nature Center
Spring Schedule
Sunday May 03
8:30—10:00 PM
Volume 35 Number 04
APRIL 2009
Report from the Officers:
With the break et al., there was
no meeting in March, but those of
you who had the chance to attend the talk by Dr. James Kennet heard a very controversial
interpretation of data from recent
prehistory: a comet exploded
Astronomy Day
Saturday May 02
Lawrence Public Library
Noon to 3PM
MONTHLY MEETINGS
Friday, APRIL 17, 2009
7:30 PM—2001 Malott Hall
Dr. Steve Hawley
President:
Rick Heschmeyer
[email protected]
Treasurer:
Dr. Steve Shawl
[email protected]
University Advisor:
Dr. Bruce Twarog
[email protected]
Webmaster:
Gary Webber
[email protected]
Observing Clubs
Doug Fay
[email protected]
over North America about
13,000 years ago, causing a
long bout of climate cooling.
The extraterrestrial impact
supposedly explains massive
The HST in Operation
mammal die-offs and the demise of one of the earliest American cultures (Clovis). It would also be the
first known extraterrestrial impact to affect modern humans.
In April, our speaker will be no less exciting but somewhat less controversial, Dr.
Steve Hawley, former astronaut and now professor of Physics and Astronomy at
KU. In keeping with our theme of telescopes and the International Year of Astronomy, Dr. Hawley will give a presentation on My Life with the Hubble Space Telescope. This talk was selected because Steve was a key participant in the deployment and maintenance of HST and the next repair mission is scheduled for launch in
(Continued on page 2)
Of Local Interest : As Science Evolves, So Does Pluto
Space.com
Pluto's status nowadays as a so-called plutoid and former planet may be official in
the latest textbooks, but someone forgot to tell the astronomers. A panel of six of
them gathered here last Tuesday to debate the former ninth planet's status at the
American Museum of Natural History, along with moderator Neil Tyson.
INSIDE THIS ISSUE
45th IAYC
2
Pluto (cont.)
3
NASA Space Place
4
Hubble Finds SN Progenitor
5
APRIL MEETING POSTER
6
Spitzer Captures Merger
7
First Gamma-Ray-Only Pulsar
8
Hubble Find (continued)
9
Black Hole Self-Regulation
9
Public interest in poor Pluto has peaked ever since the International Astronomical
Union demoted Pluto from planet status in 2006. And it became clear at the museum
event that fierce disagreement still exists among top scientists at the leading edge of
the debate. The panelists said they remained dissatisfied with the IAU decision,
which if anything has only intensified the debate and confused the public with politics
amidst uncertainty.
"The IAU vote was really a political action to the Pluto huggers and Pluto haters,"
said Mark Sykes, director of the Planetary Science Institute in Tucson, Ariz., who has
led criticism of the IAU's decision.
The face-off reaches back at least several years further. As director of the American
Museum of Natural History's (AMNH) Hayden Planetarium, Tyson found himself facing an outcry from astronomers, science educators and students when the museum
(Continued on page 2)
2
(Continued from page 1)
May 2009. Steve is an exceptionally entertaining speaker, so please keep Friday April 17 open on your
calendar and bring a friend along to the talk.
The public observing session (MARCH 29) went off on schedule, though the late departure of the cloud
cover and the cooler temperatures kept attendance to a minimum. So much for my assumption that late
March would supply warmer nights for observing. If it’s still in the 30’s for our last regular session in
early May (Sunday May 03), we will have larger issues to consider than a cancelled observing session!
Hope you can make it out for the May 03 viewing—starting after 8:30 PM and closer to 9:00 PM with the
lengthening days. With the Summer approaching, please mark your calendars for Saturday May 02 for
ASTRONOMY DAY. As we did last year, we will set up at the Lawrence Public Library from Noon to
3PM. Please contact Rick if you can help. Finally, speaking of Summer, it appears from the Parks and Rec Summer/Fall catalog
that Lawrence City Band Concerts are still on for the Summer. The dates are May 27, June10, June 24, and July 8. We are planning to do post-concert public observing in South Park from 9-10:30 PM, weather-permitting. More details in the next newsletter.
Look forward to seeing everyone at the Friday, April 17 meeting.
45th International Astronomical Youth Camp
The International Astronomical Youth Camp (IAYC) 2009 will take place in southern Poland, near the small town of Korbielow at Schronisko na
Hala Miziowa, a mountain hotel in the Beskid Zywiecki district which is part of the outer Eastern Carpathians. The house is situated close to the
1557 meter high Pilsko mountain being the second highest peak in the region, and to the Slovakian border. The IAYC is an international youth
camp with participants from about 20 different countries. As a participant you work for three weeks in one of the 8 working groups - together with
other young people - on astronomical projects. The projects vary from night-time observations to theoretical problems, depending on your own
interests. The working groups will be led by young scientists from the IAYC team. The IAYC 2009 will offer a wide range of working groups and
topics, ranging from ancient astronomy, introduction to astronomy and physics and practical observation groups to computer simulations, CCD
photometry and data reduction; there will be something for everyone from the very beginner to the ambitious student. Anyone from 16 to 24 years
old and able to communicate in English may participate in the IAYC 2009. For details, see http://www.iayc.org/next/.
(Continued from page 1)
opened a new solar system exhibit in 2000 that intentionally omitted Pluto as one of the planets. Tuesday evening's conversation
revealed how uncertainty can breed politics in science — but also how scientists deal with an evolving understanding of the universe.
Many people involved in the Pluto debate fall roughly into two camps. One side argues that Pluto, which sits far out beyond the
eight current planets, belongs with the icy Kuiper Belt Objects that it hangs out with beyond Neptune. The other side says that
Pluto's characteristics distinguish it from lesser bodies in the solar system, and so it deserves the planet moniker. The International Astronomical Union (IAU) first demoted Pluto to a "dwarf planet" in 2006 after the discovery of Eris, a Kuiper Belt Object
larger than Pluto. Last year the IAU went further by reclassifying Pluto as a plutoid, essentially ruling out Pluto's planetary status
because it sits beyond Neptune and fails to clear out asteroids and other smaller debris from its orbital neighborhood.
Many of the astronomers and astrophysicists at the recent debate agreed that the IAU's use of the word "clear" was confusing,
because not even Jupiter completely clears its neighborhood. Instead, they suggested that Pluto does not "gravitationally dominate" its neighborhood like planets such as Earth, Jupiter or even Mercury. "Classification is meant to facilitate communication
between scientists," said Steven Soter, a planetary scientist at AMNH who co-hosted the "Cosmos" television series with Carl
Sagan. "Now about clearing, that was an unfortunate term, because planets never fully clear their orbits."
But the museum panel strongly disagreed on whether or not to include Pluto, Eris and other round Kuiper Belt Objects as planets.
Soter said that he agreed with the idea of partly defining planets by where they hang out in the solar system, which brought an
immediate response from other astronomers." By the IAU's definition, when a cowboy herds his cattle he becomes a cow by asso(Continued on page 3)
About the Astronomy Associates of Lawrence
The club is open to all people interested in sharing their love for astronomy. Monthly meetings are typically on the second Friday of
each month and often feature guest speakers, presentations by club members, and a chance to exchange amateur astronomy tips.
Approximately the last Sunday of each month we have an open house at the Prairie Park Nature Center. Periodic star parties are
scheduled as well. For more information, please contact the club officers:our president, Rick Heschmeyer at [email protected],
our webmaster, Gary Webber, at [email protected], or our faculty advisor, Prof. Bruce Twarog at [email protected] Because of the
flexibility of the schedule due to holidays and alternate events, it is always best to check the Web site for the exact Fridays and
Sundays when events are scheduled. The information about AAL can be found at
http://www.ku.edu/~aal.
Copies of the Celestial Mechanic can also be found on the web at
http://www.ku.edu/~aal/celestialmechanic
3
(Continued from page 2)
ciation," said Alan Stern, a planetary scientist and former NASA science director who was deemed "Mr. Pluto" by
Tyson. "This is why I like characteristics and not association."
Stern wondered at the absurdity of a definition that would exclude an Earth-like object with "oceans, continents, blue
sky, people and Broadway lights" if it sat beyond a certain distance in the solar system. The idea of what counts
as a planet becomes even less certain beyond Earth's solar system, where space telescopes have uncovered
more than 300 exoplanets orbiting stars other than the sun. "No one is writing a law or rule that you have to call them
this or that," said Sara Seager, an astrophysicist at MIT.
She pointed out that while most attention has focused on the lower limit of the planet debate with Pluto, scientists
also fiercely debate the upper limit where a planet becomes a star. A star is typically defined by being able to carry
out fusion, but some super-massive brown dwarfs and other objects blur current planetary definitions. "People have
some cutoff they like, but lo and behold, astronomers discovered three planets orbiting a central star," Seager noted.
"According to the IAU, they can't be planets because they're too massive."
And if defining a planet by its characteristics can run into some difficulties, defining planets by location gets even
trickier. Tyson wondered about objects known as "planemos," or "rogue planets" that float through space without a
star to orbit. "Why not have a classification scheme starting with planemos ... I don't really like that word," Tyson
mused.
Gibor Basri, an astrophysicist at the University of California-Berkeley, chimed in. "It didn't really catch on," said Basri,
who coined the term. Uncertainty aside, all of the panel members spoke eagerly of NASA's Kepler space telescope,
which launched on March 7. That mission is designed to search for signs of smaller, rocky planets like Earth among
over 100,000 stars.
"Let me be bold and say that perhaps planetary science is still in its infancy, and has no business classifying anything at all yet," Tyson said, noting that new data from Kepler's survey could change the debate down the road.
The whole debacle has painted a new picture of how planetary scientists operate. "I think this has been one of the
more disappointing episodes for science with regard to the IAU," Stern said. "Now school kids see science as voting,
and that's not the best way to do science." "I like to call it the Irrelevant Astronomical Union," Stern added. He
summed up the messiness of the scientific process as being "like cats herding themselves."
Basri agreed that "whenever you get a [scientific] issue decided by a vote, I think you can infer that people don't
know what they're talking about." He observed that scientists did not vote on the existence of gravity.
All the arguments can also hide the fact that scientists continue to do research and pursue new knowledge, Seager
suggested. "I'm not calling Alan [Stern] and saying, 'What do you think today, is it a planet?'" she said. The science
may remain far from settled on Pluto and other planets, but the panelists also saw a bright side in the mess.
"The best thing about this debate is that it got people interested and became a teaching moment," said Jack Lissauer, a theoretical physicist at NASA's Ames Research Center in California. Much of the original controversy over
Pluto's demotion may stem from how science has been taught in schools, Tyson said. He criticized the idea of
branding facts into the brains of young schoolchildren, given that science remains a dynamic and ever-changing
process.
"I see this as maybe a rare moment to see the birth of a new way of thinking about the solar system and the richness
of objects that orbit it," Tyson said. He recalled recent letters from third graders born in 2000 who are now "kind of
OK with Pluto being something other than the ninth planet," because they grew up with Pluto's planetary status already in question.
Seager mentioned that she had kids just starting school at a time when the "whole toy industry has already dropped
Pluto," but also expressed confidence that students would be okay with a changing understanding of the solar system.
After all, the panelists suggested, it's perhaps more important to love the scientific process rather than the scientific
facts.
"I'm one of the people who don't characterize Pluto as a planet," Lissauer said, drawing applause as he brought out
a Disney "Pluto" stuffed toy. "But I care about solar system objects, and I am a Pluto hugger."
4
Apollo Upgrade
The flight computer onboard the Lunar Excursion Module, which landed on the Moon during the Apollo program, had a whopping 4 kilobytes of RAM and a 74-kilobyte “hard drive.” In places, the craft’s outer skin was as thin as two sheets of aluminum
foil.
It worked well enough for Apollo. Back then, astronauts needed to stay on the Moon for only a few days at a time. But when
NASA once again sends people to the Moon starting around 2020, the plan will be much more ambitious—and the hardware is
going to need a major upgrade.
“Doing all the things we want to do using systems from Apollo would be very risky and perhaps not even possible,” says Frank
Peri, director of NASA’s Exploration Technology Development Program.
So the program is designing new, more capable hardware and software to meet the demands of NASA’s plan to return humans to
the moon. Instead of staying for just a few days, astronauts will be living on the Moon’s surface for months on end. Protecting
astronauts from harsh radiation at the Moon’s surface for such a long time will require much better radiation shielding than just a
few layers of foil. And rather than relying on food and water brought from Earth and jettisoning urine and other wastes, new life
support systems will be needed that can recycle as much water as possible, scrub carbon dioxide from the air without depending
on disposable filters, and perhaps grow a steady supply of food—far more than Apollo life-support systems could handle.
Next-generation lunar explorers will perform a much wider variety of scientific research, so they’ll need vehicles that can carry
them farther across the lunar surface. ETDP is building a new lunar rover that outclasses the Apollo-era moon buggy by carrying
two astronauts in a pressurized cabin. “This vehicle is like our SUV for the Moon,” Peri says.
The Exploration Technology Development Program is also designing robots to help astronauts maintain their lunar outpost and
perform science reconnaissance. Making the robots smart enough to take simple verbal orders from the astronauts and carry out
their tasks semi-autonomously requires vastly more powerful computer brains than those on Apollo; four kilobytes of RAM just
won’t cut it.
The list goes on: New rockets
to carry a larger lunar lander,
spacesuits that can cope with
abrasive moon dust, techniques
for converting lunar soil into
building materials or breathable
oxygen. NASA’s ambitions for
the Moon have been upgraded.
By tapping into 21st century
technology, this program will
ensure that astronauts have the
tools they need to turn those
ambitions into reality.
The Chariot Lunar Truck is one idea for a vehicle equal to the lunar terrain. Each of the six
wheels pivot in any direction, and two turrets allow the astronauts to rotate 360°.
Learn more about the Exploration Technology Development
Program at www.nasa.gov/
directorates/esmd/aboutesmd/
acd/ technology_ dev.html.
Kids can build their own Moon
habitat at spaceplace.nasa.gov/
en/kids/exploration/habitat.
This article was provided by
the Jet Propulsion Laboratory,
California Institute of Technology, under a contract with the
National Aeronautics and
Space Administration.
5
Hubble Finds Rare Progenitor to a Supernova
NASA's Hubble Space Telescope has identified a star that was one million times brighter than the sun before it
exploded as a supernova in 2005. According to current theories of stellar evolution, the star should not have selfdestructed so early in its life. "This might mean that we are fundamentally wrong about the evolution of massive
stars, and that theories need revising," says Avishay Gal-Yam of the Weizmann Institute of Science, Rehovot,
Israel.
The doomed star, which is estimated to have weighed about 100 times our sun's mass, was not mature enough,
according to theory, to have evolved a massive iron core of nuclear fusion ash. This is the prerequisite for a core
implosion that triggers a supernova blast.
The finding appears in the online version of Nature Magazine.
The explosion, called supernova SN 2005gl,
was seen in the barred-spiral galaxy NGC
266 on October 5, 2005. Pre-explosion pictures from the Hubble archive, taken in 1997,
reveal the progenitor as a very luminous
point source with an absolute visual magnitude of -10.3.
The progenitor was so bright that it probably
belonged to a class of stars called Luminous
Blue Variables (LBVs), "because no other
type of star is as intrinsically brilliant," says
Gal-Yam. As an LBV-class star evolves it
sheds much of its mass through a violent
stellar wind. Only at that point does it develop a large iron core and ultimately explodes as a core-collapse supernova.
Extremely massive and luminous stars topping 100 solar masses, such as Eta Carinae
in our own Milky Way Galaxy, are expected
to lose their entire hydrogen envelopes prior
to their ultimate explosions as supernovae.
"These observations demonstrate that many
details in the evolution and fate of LBVs remain a mystery. We should continue to keep
an eye on Eta Carinae, it may surprise us yet
again," says supernova expert Mario Livio of
the Space Telescope Science Institute, Baltimore, Md.
"The progenitor identification shows that, at least in some cases, massive stars explode before losing most of
their hydrogen envelope, suggesting that the evolution of the core and the evolution of the envelope are less coupled than previously thought, a finding which may require a revision of stellar evolution theory," says co-author
Douglas Leonard from San Diego State University, Calif.
One possibility is that the progenitor to SN 2005gl was really a pair of stars, a binary system that merged. This
would have stoked nuclear reactions to brighten the star enormously, making it look more luminous and less
evolved than it really is. "This also leaves open the question that there may be other mechanisms for triggering
supernova explosions," says Gal-Yam. "We may be missing something very basic in understanding how a superluminous star goes through mass loss."
Gal-Yam reports that the observation revealed that only a small part of the star's mass was flung off in the explosion. Most of the material, says Gal-Yam, was drawn into the collapsing core that has probably become a black
hole estimated to be at least 10 to 15 solar masses.
(Continued on page 9)
6
7
SPITZER CAPTURES MERGING GALAXIES
A new image from NASA's Spitzer Space Telescope offers a rare view of an imminent collision between the cores of
two merging galaxies, each powered by a black hole with millions of times the mass of the sun.
The galactic cores are in a single, tangled galaxy called NGC 6240, located 400-million light years away in the constellation Ophiuchus. Millions of years ago, each core was the dense center of its own galaxy before the two galaxies collided and ripped each other apart. Now, these cores are approaching each other at tremendous speeds and preparing
for the final cataclysmic collision. They will crash into each other in a few million years, a relatively short period on a
galactic timescale.
The spectacular image combines visible light from NASA's Hubble Space Telescope and infrared light from Spitzer. It
catches the two galaxies during a rare, short-lived phase of their evolution, when both cores of the interacting galaxies
are still visible but closing in on each other fast.
"One of the most exciting things about the
image is that this object is unique," said
Stephanie Bush of the Harvard-Smithsonian
Center for Astrophysics, Cambridge, Mass.,
lead author of a new paper describing the
observation in an upcoming issue of the Astrophysical Journal. "Merging is a quick process, especially when you get to the train
wreck that is happening. There just aren't
many galactic mergers at this stage in the
nearby universe."
NGC 6240 is already putting out huge
amounts of infrared light, an indication that a
burst of star formation is underway. The extra
infrared radiation is common in interacting
galaxies; as the two galaxies interact, dust
and gas swept up by the collision form a
burst of new stars that give off infrared light.
Such galaxies are called luminous infrared
galaxies. Spitzer's infrared array camera can
image the extra heat from newly formed
stars, even though their visible light is obscured by thick dust clouds around them. The
blob-like shape of the galaxy is due to the
sustained violence of the collision. Streams of
millions of stars are being ripped off the galaxy, forming wispy "tidal tails" that lead off
NGC 6240 in several directions. But things
are about to get even more violent as the
main event approaches and the two galactic
cores meld into one.
In the center of NGC 6240, the two black
holes in the cores will whip up a frenzy of
radiation as they careen towards one another
head-on, likely transforming the galaxy into a monster known as an ultra-luminous infrared galaxy, thousands of times
as bright in infrared as our Milky Way.
Another fascinating aspect of this rare object is that no two galactic mergers are the same. "Not only are there few objects at this stage, but each object is unique because it came from different progenitor galaxies," said Bush. "These
observations give us another layer of information about this galaxy, and galactic mergers in general." Infrared light
taken by Spitzer's infrared array camera at 3.6 and 8.8 microns (red) shows cold dust and radiation from star formation; visible light from Hubble (green and blue) shows hot gas and stars.
8
NASA'S Fermi Telescope Discovers First Gamma-Ray-Only Pulsar
About three times a second, a 10,000-year-old stellar corpse sweeps a beam of gamma-rays toward Earth. Discovered
by NASA's Fermi Gamma-ray Space Telescope, the object, called a pulsar, is the first one known that only "blinks" in
gamma rays.
"This is the first example of a new class of pulsars that will give us fundamental insights into how these collapsed stars
work," said Stanford University's Peter Michelson, principal investigator for Fermi's Large Area Telescope in Palo Alto,
Calif.
The gamma-ray-only pulsar lies within a supernova remnant known as CTA 1, which is located about 4,600 light-years
away in the constellation Cepheus. Its lighthouse-like beam sweeps Earth's way every 316.86 milliseconds. The pulsar,
which formed about 10,000 years ago, emits 1,000 times the energy of our sun.
A pulsar is a rapidly spinning neutron star, the crushed core left behind when a massive sun explodes. Astronomers have cataloged
nearly 1,800 pulsars. Although most were found through their pulses
at radio wavelengths, some of these objects also beam energy in
other forms, including visible light and X-rays. However, the source in
CTA 1 only pulses at gamma-ray energies.
"We think the region that emits the pulsed gamma rays is broader
than that responsible for pulses of lower-energy radiation," explained
team member Alice Harding at NASA's Goddard Space Flight Center
in Greenbelt, Md. "The radio beam probably never swings toward
Earth, so we never see it. But the wider gamma-ray beam does
sweep our way."
Scientists think CTA 1 is only the first of a large population of similar
objects.
"The Large Area Telescope provides us with a unique probe of the galaxy's pulsar population, revealing objects we
would not otherwise even know exist," says Fermi project scientist Steve Ritz, also at Goddard.
The pulsar in CTA 1 is not located at the center of the remnant's expanding gaseous shell. Supernova explosions can
be asymmetrical, often imparting a "kick" that sends the neutron star careening through space. Based on the remnant's
age and the pulsar's distance from its center, astronomers believe the neutron star is moving at about a million miles per hour -- a typical speed.
Fermi's Large Area Telescope scans the entire sky every
three hours and detects photons with energies ranging
from 20 million to more than 300 billion times the energy
of visible light. The instrument sees about one gamma
ray every minute from CTA 1, enough for scientists to
piece together the neutron star's pulsing behavior, its
rotation period, and the rate at which it is slowing down.
A pulsar's beams arise because neutron stars possess
intense magnetic fields and rotate rapidly. Charged particles stream outward from the star's magnetic poles at
nearly the speed of light to create the gamma-ray beams
Fermi sees. Because the beams are powered by the
neutron star's rotation, they gradually slow the pulsar's
spin. In the case of CTA 1, the rotation period is increasing by about one second every 87,000 years.
"This observation shows the power of the Large Area
Telescope," Michelson said. "It is so sensitive that we
can now discover new types of objects just by observing
their gamma-ray emissions."
9
Erratic Black Hole Regulates Itself
New results from NASA's Chandra X-ray Observatory have made a major advance in explaining how a special
class of black holes may shut off the high-speed jets they produce. These results suggest that these black holes
have a mechanism for regulating the rate at which they grow.
Black holes come in many sizes: the supermassive ones, including those in quasars, which weigh in at millions to billions of times the mass of the Sun, and the much smaller stellar-mass black holes which have measured
masses in the range of about 7 to 25 times the Sun's mass. Some stellar-mass black holes launch powerful jets of
particles and radiation, like seen in quasars, and are called "micro-quasars". The new study looks at a famous micro-quasar in our own Galaxy, and regions close to its event horizon, or point of no return. This system, GRS
1915+105 (GRS 1915 for short), contains a black hole about 14 times the mass of the Sun that is feeding off material from a nearby companion star. As the material swirls toward the black hole, an accretion disk forms.
This system shows remarkably unpredictable and complicated variability ranging from timescales of seconds
to months, including 14 different patterns of variation. These variations are caused by a poorly understood connection between the disk and the radio jet seen in GRS 1915. Chandra, with its spectrograph, has observed GRS 1915
eleven times since its launch in 1999. These studies reveal that the jet in GRS 1915 may be periodically choked off
when a hot wind, seen in X-rays, is driven off the accretion disk around the black hole. The wind is believed to shut
down the jet by depriving it of matter that would have otherwise fueled it. Conversely, once the wind dies down, the
jet can re-emerge. "We think the jet and wind around this black hole are in a sort of tug of war," said Joseph Neilsen, Harvard graduate student and lead author of the paper appearing in the journal Nature. "Sometimes one is
winning and then, for reasons we don't entirely understand, the other one gets the upper hand."
The latest Chandra results also show that the wind and the jet carry about the same amount of matter away
from the black hole. This is evidence that the black hole is somehow regulating its accretion rate, which may be
related to the toggling between mass expulsion via either a jet or a wind from the accretion disk. Self-regulation is a
common topic when discussing supermassive black holes, but this is the first clear evidence for it in stellar-mass
black holes. "It is exciting that we may be on the track of explaining two mysteries at the same time: how black hole
jets can be shut down and also how black holes regulate their growth," said co-author Julia Lee, assistant professor
in the Astronomy department at the Harvard-Smithsonian Center for Astrophysics. "Maybe black holes can regulate
themselves better than the financial markets!"
Although micro-quasars and quasars differ in mass by factors of millions, they should show a similarity in behavior when their very different physical scales are taken into account. "If quasars and micro-quasars behave very
differently, then we have a big problem to figure out why, because gravity treats them the same," said Neilsen. "So,
our result is actually very reassuring, because it's one more link between these different types of black holes." The
timescale for changes in behavior of a black hole should vary in proportion to the mass. For example, an hour-long
timescale for changes in GRS 1915 would correspond to about 10,000 years for a supermassive black hole that
weighs a billion times the mass of the Sun. "We cannot hope to explore at this level of detail in any single supermassive black hole system," said Lee. "So, we can learn a tremendous amount about black holes by just studying
stellar-mass black holes like this one.
It is not known what causes the jet to turn on again once the wind dies down, and this remains one of the
major unsolved mysteries in astronomy. "Every major observatory, ground and space, has been used to study this
black hole for the past two decades," said Neilsen. "Although we still don't have all the answers, we think our work
is a step in the right direction."
(Continued from page 5)
Gal-Yam and Leonard located the progenitor in archival images of NGC 266 taken in 1997. It was easily identifiable
only because it is so superluminous. Only Hubble could clearly resolve it at such a great distance.
The team then used the Keck telescope to precisely locate the supernova on the outer arm of the galaxy. A followup observation with Hubble in 2007 unequivocally showed that the superluminous star was gone. To make sure the
new observation was consistent with the 1997 archival image, the astronomers used the same Hubble camera used
in 1997, the Wide Field Planetary Camera 2.
Finding archival images of stars before the stars explode as supernovae isn't an easy task. Several other supernova progenitor candidates have been reported prior to the Hubble observation. The only other absolutely indisputable progenitor, however, was the blue supergiant progenitor to SN 1987A. In the case of SN 1987A, it was thought
that the progenitor star was once a red supergiant and at a later stage evolved back to blue supergiant status. This
led to a major reworking of supernova theory. The progenitor star observed by Gal-Yam is too massive to have
gone through such an oscillation to the red giant stage, so yet another new explanation is required, he says.
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Celestial Mechanic April 2009
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