A research team led by Alex Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State, who discovered the first planets ever found outside our solar system, has discoverwed three new planets with the Hobby-Eberly Telescope. Penn State is a major partner in this telescope, which is one of the largest in the world. |
Three
planets—each orbiting its own giant, dying star—have been discovered by
an international research team led by a Penn State University
astronomer. Using the Hobby-Eberly Telescope, the astronomers observed
the planets’ parent stars—called HD 240237, BD +48 738, and HD
96127—tens of light years away from our solar system. One of the
massive, dying stars has an additional mystery object orbiting it,
according to team leader Alexander Wolszczan, Evan Pugh Professor of
Astronomy and Astrophysics at Penn State, who, in 1992, became the first
astronomer ever to discover planets outside our solar system. The new
research is expected to shed light on the evolution of planetary systems
around dying stars. It also will help astronomers to understand how
metal content influences the behavior of dying stars.
The
research will be published in December in the Astrophysical Journal.
The first author of the paper is Sara Gettel, a graduate student from
Penn State’s Department of Astronomy and Astrophysics, and the paper is
co-authored by three graduate students from Poland.
The three newly discovered planetary systems are more evolved than our own solar system.
“Each
of the three stars is swelling and has already become a red giant—a
dying star that soon will gobble up any planet that happens to be
orbiting too close to it,” Wolszczan said. “While we certainly can
expect a similar fate for our own Sun, which eventually will become a
red giant and possibly will consume our Earth, we won’t have to worry
about it happening for another 5 billion years.”
Wolszczan
also said that one of the massive, dying stars—BD +48 738—is
accompanied not only by an enormous, Jupiter-like planet, but also by a
second, mystery object.
According
to the team, this object could be another planet, a low-mass star,
or—most interestingly—a brown dwarf, which is a star-like body that is
intermediate in mass between the coolest stars and giant planets.
“We
will continue to watch this strange object and, in a few more years, we
hope to be able to reveal its identity,” Wolszczan said.
The
three dying stars and their accompanying planets have been particularly
useful to the research team because they have helped to illuminate such
ongoing mysteries as how dying stars behave depending on their
metallicity.
“First,
we know that giant stars like HD 240237, BD +48 738, and HD 96127 are
especially noisy. That is, they appear jittery, because they oscillate
much more than our own, much-younger Sun. This noisiness disturbs the
observation process, making it a challenge to discover any companion
planets,” Wolszczan said. “Still, we persevered and we eventually were
able to spot the planets orbiting each massive star.”
Once
Wolszczan and his team had confirmed that HD 240237, BD +48 738 and HD
96127 did indeed have planets orbiting around them, they measured the
metal content of the stars and found some interesting correlations.
“We
found a negative correlation between a star’s metallicity and its
jitteriness. It turns out that the less metal content each star had, the
more noisy and jittery it was,” Wolszczan explained. “Our own Sun
vibrates slightly too, but because it is much younger, its atmosphere is
much less turbulent.”
Wolszczan
also pointed out that, as stars swell to the red-giant stage, planetary
orbits change and even intersect, and close-in planets and moons
eventually get swallowed and sucked up by the dying star. For this
reason, it is possible that HD 240237, BD +48 738 and HD 96127 once
might have had more planets in orbit, but that these planets were
consumed over time.
“It’s
interesting to note that, of these three newly-discovered stars, none
has a planet at a distance closer than 0.6 astronomical units—that is,
0.6 the distance of the Earth to our Sun,” Wolszczan said. “It might be
that 0.6 is the magic number at which any closer distance spells a
planet’s demise.”
Observations
of dying stars, their metal content, and how they affect the planets
around them could provide clues about the fate of our own solar system.
“Of
course, in about 5 billion years, our Sun will become a red giant and
likely will swallow up the inner planets and the planets’ accompanying
moons. However, if we’re still around in, say, 1 billion to 3 billion
years, we might consider taking up residence on Jupiter’s moon, Europa,
for the remaining couple billion years before that happens,” Wolszczan
said. “Europa is an icy wasteland and it is certainly not habitable now,
but as the Sun continues to heat up and expand, our Earth will become
too hot, while at the same time, Europa will melt and may spend a couple
billion years in the Goldilocks zone—not to hot, not to cold—covered by
vast, beautiful oceans.”
Penn
State’s Center for Exoplanets and Habitable Worlds is organizing a
conference in January 2012 to discuss planets and their dying stars. The
conference will be held in Puerto Rico and is scheduled to take place
at exactly 20 years from when Wolszczan used the 1,000-foot Arecibo
radiotelescope to detect three planets orbiting a rapidly spinning
neutron star—the very first discovery of planets outside our solar
system. This discovery opened the door to the current intense era of
planet hunting by suggesting that planet formation could be quite common
throughout the universe and that planets can form around different
types of stellar objects. Information about the conference is online at http://www.mpia-hd.mpg.de/PLANETS2012/index.html.
In
addition to Wolszczan and Gettel at Penn State, other members of the
research team include Andrzej Niedzielski, Gracjan Maciejewski, and
three graduate students: Grzegorz Nowak, Monika Adamow, and Pawel
Zielinski, who all are from Nicolaus Copernicus University in Torun,
Poland.
Funding for this research was provided by NASA and the Polish Ministry of Science and Higher Education.
