The LHCb collaboration has reported an intriguing new result in its
quest to test a key principle of the Standard Model called lepton
universality. Although not statistically significant, the finding—a
possible difference in the behavior of different types of lepton
particles—chimes with other previous results. If confirmed, as more data
are collected and analyzed, the results would signal a crack in the
Standard Model.
Lepton
universality is the idea that all three types of charged lepton
particles—electrons, muons and taus—interact in the same way with other
particles. As a result, the different lepton types should be created
equally often in particle transformations, or "decays," once differences
in their mass are accounted for. However, some measurements of particle
decays made by the LHCb team and other groups over the past few years
have indicated a possible difference in their behavior. Taken
separately, these measurements are not statistically significant enough
to claim a breaking of lepton universality and hence a crack in the
Standard Model, but it is intriguing that hints of a difference have
been popping up in different particle decays and experiments.
The latest LHCb result
is the first test of lepton universality made using the decays of
beauty baryons—three-quark particles containing at least one beauty
quark. Sifting through proton–proton collision data at energies of 7, 8
and 13 TeV, the LHCb researchers identified beauty baryons called Λb0
and counted how often they decayed to a proton, a charged kaon and
either a muon and antimuon or an electron and antielectron.
The team then took the ratio between these two decay rates. If lepton
universality holds, this ratio should be close to 1. A deviation from
this prediction could therefore signal a violation of leptonuniversality.
Such a violation could be caused by the presence in the decays of a
never-before-spotted particle not predicted by the Standard Model.
The team obtained a ratio slightly below 1 with a statistical significance of about 1 standard deviation, well below the 5 standard deviations needed to claim a real difference in the decay rates.
The researchers say that the result points in the same direction as
other results, which have observed hints that decays to a muon–antimuon
pair occur less often than those to an electron–antielectron pair, but
they also stress that much more data is needed to tell whether this
oddity in the behavior of leptons is here to stay or not.
On the left is an image of the Sombrero galaxy (M104) that includes a
portion of the much fainter halo far outside its bright disk and bulge.
Hubble photographed two regions in the halo (one of which is shown by
the white box). The images on the right zoom in to show the level of
detail Hubble captured. The orange box, a small subset of Hubble's view,
contains myriad halo stars. The stellar population increases in density
closer to the galaxy's disk (bottom blue box). Each frame contains a
bright globular cluster of stars, of which there are many in the
galaxy's halo. The Sombrero's halo contained more metal-rich stars than
expected, but even stranger was the near-absence of old, metal-poor
stars typically found in the halos of massive galaxies. Many of the
globular clusters, however, contain metal-poor stars. A possible
explanation for the Sombrero's perplexing features is that it is the
product of the merger of massive galaxies billions of years ago, even
though the smooth appearance of the galaxy's disk and halo show no signs
of such a huge disruption. Credit: NASA/Digitized Sky Survey/P.
Goudfrooij (STScI)/The Hubble Heritage Team (STScI/AURA)
Surprising new data from NASA's Hubble Space Telescope suggests the
smooth, settled "brim" of the Sombrero galaxy's disk may be concealing a
turbulent past. Hubble's sharpness and sensitivity resolves tens of
thousands of individual stars in the Sombrero's vast, extended halo, the
region beyond a galaxy's central portion, typically made of older
stars. These latest observations of the Sombrero are turning
conventional theory on its head, showing only a tiny fraction of older,
metal-poor stars in the halo, plus an unexpected abundance of metal-rich
stars typically found only in a galaxy's disk, and the central bulge.
Past major galaxy mergers are a possible explanation, though the stately
Sombrero shows none of the messy evidence of a recent merger of massive
galaxies.
"The Sombrero has always been a bit of a weird galaxy, which is what
makes it so interesting," said Paul Goudfrooij of the Space Telescope
Science Institute (STScI), Baltimore, Maryland. "Hubble's metallicity
measurements (i.e., the abundance of heavy elements in the stars) are
another indication that the Sombrero has a lot to teach us about galaxy
assembly and evolution."
"Hubble's observations of the Sombrero's halo
are turning our generally accepted understanding of galaxy makeup and
metallicity on its head," added co-investigator Roger Cohen of STScI.
Long a favorite of astronomers and amateur sky watchers alike for its
bright beauty and curious structure, the Sombrero galaxy (M104) now has
a new chapter in its strange story—an extended halo of metal-rich stars
with barely a sign of the expected metal-poor stars that have been
observed in the halos of other galaxies. Researchers, puzzling over the
data from Hubble, turned to sophisticated computer models to suggest
explanations for the perplexing inversion of conventional galactic
theory. Those results suggest the equally surprising possibility of
major mergers in the galaxy's past, though the Sombrero's majestic
structure bears no evidence of recent disruption. The unusual findings
and possible explanations are published in the Astrophysical Journal.
"The absence of metal-poor stars was a big surprise," said
Goudfrooij, "and the abundance of metal-rich stars only added to the
mystery."
In a galaxy's halo astronomers expect to find earlier generations of stars with less heavy elements,
called metals, as compared to the crowded stellar cities in the main
disk of a galaxy. Elements are created through the stellar "lifecycle"
process, and the longer a galaxy has had stars going through this cycle,
the more element-rich the gas and the higher-metallicity the stars that
form from that gas. These younger, high-metallicity stars are typically
found in the main disk of the galaxy where the stellar population is
denser—or so goes the conventional wisdom.
Complicating the facts is the presence of many old, metal-poor globular clusters of stars. These older, metal-poor stars
are expected to eventually move out of their clusters and become part
of the general stellar halo, but that process seems to have been
inefficient in the Sombrero galaxy. The team compared their results with
recent computer simulations to see what could be the origin of such
unexpected metallicity measurements in the galaxy's halo.
The results also defied expectations, indicating that the unperturbed
Sombrero had undergone major accretion, or merger, events billions of
years ago. Unlike our Milky Way galaxy, which is thought to have
swallowed up many small satellite galaxies in so-called "minor"
accretions over billions of years, a major accretion is the merger of
two or more similarly massive galaxies that are rich in
later-generation, higher-metallicity stars.
The satellite galaxies only contained low-metallicity stars that were
largely hydrogen and helium from the big bang. Heavier elements had to
be cooked up in stellar interiors through nucleosynthesis and
incorporated into later-generation stars. This process was rather
ineffective in dwarf galaxies such as those around our Milky Way, and
more effective in larger, more evolved galaxies.
The results for the Sombrero are surprising because its smooth disk
shows no signs of disruption. By comparison, numerous interacting
galaxies, like the iconic Antennae galaxies, get their name from the
distorted appearance of their spiral arms due to the tidal forces of
their interaction. Mergers of similarly massive galaxies
typically coalesce into large, smooth elliptical galaxies with extended
halos—a process that takes billions of years. But the Sombrero has
never quite fit the traditional definition of either a spiral or an
elliptical galaxy. It is somewhere in between—a hybrid.
For this particular project, the team chose the Sombrero mainly for
its unique morphology. They wanted to find out how such "hybrid"
galaxies might have formed and assembled over time. Follow-up studies
for halo metallicity distributions will be done with several galaxies at distances similar to that of the Sombrero.
The research team looks forward to future observatories continuing
the investigation into the Sombrero's unexpected properties. The Wide
Field Infrared Survey Telescope (WFIRST), with a field of view 100 times
that of Hubble, will be capable of capturing a continuous image of the
galaxy's halo while picking up more stars
in infrared light. The James Webb Space Telescope will also be valuable
for its Hubble-like resolution and deeper infrared sensitivity.
Fuente: https://phys.org/news/2020-02-brim-sombrero-galaxy-halo-turbulent.html
This Hubble Space Telescope photograph showcases the
majestic spiral galaxy UGC 2885, located 232 million light-years away in
the northern constellation Perseus. The galaxy is 2.5 times wider than
our Milky Way and contains 10 times as many stars. A number of
foreground stars in our Milky Way can be seen in the image, identified
by their diffraction spikes. The brightest star photobombs the galaxy's
disk. The galaxy has been nicknamed "Rubin's Galaxy," after astronomer
Vera Rubin (1928 – 2016), who studied the galaxy's rotation rate in
search of dark matter. Credit: NASA, ESA, and B. Holwerda (University of
Louisville)
Galaxies are like snowflakes. Though the universe contains
innumerable galaxies flung across time and space, no two ever look
alike. One of the most photogenic is the huge spiral galaxy UGC 2885,
located 232 million light-years away in the northern constellation,
Perseus. It's a whopper even by galactic standards. The galaxy is 2.5
times wider than our Milky Way and contains 10 times as many stars,
about 1 trillion. This galaxy has lived a quiescent life by not
colliding with other large galaxies. It has gradually bulked up on
intergalactic hydrogen to make new stars at a slow and steady pace over
many billions of years. The galaxy has been nicknamed "Rubin's galaxy,"
after astronomer Vera Rubin (1928—2016). Rubin used the galaxy to look
for invisible dark matter. The galaxy is embedded inside a vast halo of
dark matter. The amount of dark matter can be estimated by measuring its
gravitational influence on the galaxy's rotation rate.
This majestic spiral galaxy might earn the nickname the "Godzilla
Galaxy" because it may be the largest known in the local universe. The
galaxy, UGC 2885, is 2.5 times wider than our Milky Way and contains 10
times as many stars.
But it is a "gentle giant," say researchers, because it looks like it
has been sitting quietly over billions of years, possibly sipping
hydrogen from the filamentary structure of intergalactic space.
This fuels modest ongoing star birth at half the rate of our Milky Way.
In fact, its supermassive central black hole is a sleeping giant, too;
because the galaxy does not appear to be feeding on much smaller
satellite galaxies, it is starved of infalling gas.
The galaxy has been nicknamed "Rubin's galaxy," after astronomer Vera
Rubin (1928—2016) by Benne Holwerda of the University of Louisville,
Kentucky, who observed the galaxy with NASA's Hubble Space Telescope.
"My research was in a large part inspired by Vera Rubin's work in
1980 on the size of this galaxy." Rubin measured the galaxy's rotation,
which provides evidence for dark matter, which makes up most of the
galaxy's mass as measured by the rotation rate. "We consider this a
commemorative image. This goal to cite Dr. Rubin in our observation was
very much part of our original Hubble proposal."
In results being presented at the winter American Astronomical Society meeting in Honolulu, Hawaii,
Holwerda is seeking to understand what led to the galaxy's monstrous
size. "How it got so big is something we don't quite know yet," said
Holwerda. "It's as big as you can make a disk galaxy without hitting
anything else in space."
One clue is that the galaxy is fairly isolated in space and doesn't
have any nearby galaxies to crash into and disrupt the shape of its
disk.
Did the monster galaxy gobble up much smaller satellite galaxies over
time? Or did it just slowly accrete gas for new stars? "It seems like
it's been puttering along, slowly growing," Holwerda said. Using
Hubble's exceptional resolution, his team is counting the number of
globular star clusters in the galaxy's halo—a vast shell of faint stars
surrounding the galaxy. An excess of clusters would yield evidence that
they were captured from smaller infalling galaxies over many billions of
years.
NASA's upcoming James Webb Space Telescope could be used to explore
the center of this galaxy as well as the globular cluster population.
NASA's planned Wide Field Infrared Survey Telescope (WFIRST) would give
an even more complete census of this galaxy's cluster population,
especially that of the whole halo. "The infrared capability of both
space telescopes would give us a more unimpeded view of the underlying
stellar populations," said Holwerda. This complements Hubble's
visible-light ability to track wispy star formation throughout the
galaxy.
A number of foreground stars
in our Milky Way can be seen in the image, identified by their
diffraction spikes. The brightest appears to sit on top of the galaxy's
disk, though UGC 2885 is really 232 million light-years farther away.
The giant galaxy is located in the northern constellation Perseus.
Fuente:https://phys.org/news/2020-01-nasa-hubble-surveys-gigantic-galaxy.html
The CHEOPS spacecraft is taking the first tentative steps in its
mission. Back on January 29th, the spacecraft opened the cover on its
lens. Now, we have the first images from CHEOPS. CHEOPS stands for CHaracterising ExOPlanet Satellite.
It’s a European Space Agency (ESA) mission to study some of the
brightest and closest stars that are already known to host exoplanets.
CHEOPS will make precision measurements of exoplanet sizes in order to
reveal the density and composition of the worlds. It’s focusing on
planets in the super-Earth to Neptune mass range.
Don’t get too excited yet. These first images won’t win any awards.
But they’re not meant to. Their purpose is to verify that the
satellite’s systems are working, so their blurry nature is a critical
part of the mission. And as the team waited for the first images the
tension grew.
“When the first
images of a field of stars appeared on the screen, it was immediately
clear to everyone that we did indeed have a working telescope.”
Willy Benz, Principal Investigator, CHEOPS Mission.
“The
first images that were about to appear on the screen were crucial for
us to be able to determine if the telescope’s optics had survived the
rocket launch in good shape,” explains Willy Benz, Professor of
Astrophysics at the University of Bern and Principal Investigator of the
CHEOPS mission, in a press release.
“When the first images of a field of stars appeared on the screen, it
was immediately clear to everyone that we did indeed have a working
telescope,” said Benz.
First
image of the star chosen as target for CHEOPS after cover opening. The
star, at the centre of the image, is located at a distance of 150
light-years from us, in the constellation of Cancer. The image is about
1000×1000 pixels in size, with each pixel representing a tiny angle of
about 0.0003 degree (1 arcsecond) on the sky. The other, fainter stars
in the image are in the background of the target. The inset in the lower
right corner shows a region of about 100-pixels in width, centered on
the target star. The peculiar shape of the star in the image is due to
the deliberate defocusing of CHEOPS optics. CHEOPS measures the star’s
brightness by adding up the light received in all pixels within a region
centered on the star as illustrated by the circle in the picture. The
defocusing spreads the light onto many pixels, which allows CHEOPS to
reach best possible photometric precision. Image Credit:
ESA/Airbus/CHEOPS Mission Consortium
Now that
the CHEOPS team knows the telescope is working, they need to know how
well it’s working. The team has had some time to analyze the image, and
they say that CHEOPS is actually exceeding expectations. But in this
case, CHEOPS is deliberately unfocused for testing, so better doesn’t
mean clearer.
“This beautifully blurred image carries the promise of a new, deeper understanding of worlds beyond our Solar System.”
Kate Isaak, ESA Cheops Project Scientist.
“The
good news is that the actual blurred images received are smoother and
more symmetrical than what we expected from measurements performed in
the laboratory,” says Benz. The blurred testing is designed to spread
incoming light over as many pixels as possible. The results will tell
the CHEOPS team if the telescope is smoothing out its jitters and its
“pixel-to-pixel variations.” That smoothing is what will give CHEOPS its
exceptional precision.
“These initial promising analyses are a great relief and also a boost for the team.”
WILLY BENZ, PRINCIPAL INVESTIGATOR, CHEOPS MISSION.
These
tests are all about the precision that CHEOPS needs to fulfill its
mission. CHEOPS isn’t a planet-finding mission. It’s going to examine
already-known exoplanets with extreme precision. It needs to sense
extremely small dips in brightness as an exoplanet transits in front of
its star. Since it’s the size of the planet that determines that dip,
the more precisely CHEOPS can measure the dip, the more precisely it can
determine the size of the planet.
“These initial promising analyses are a great relief and also a boost for the team,” said Benz.
This is just the beginning of CHEOPS’ testing phase. Over the course
of about two months, the satellite will take more images. The overall
goal of all these tests is to determine how accurate the spacecraft can
be during different parts of its mission. “We will analyze many more
images in detail to determine the exact level of accuracy that can be
achieved by CHEOPS in the different aspects of the science program,”
said David Ehrenreich, CHEOPS project scientist at the University of
Geneva. “The results so far bode well.”
The CHEOPS mission, like all space missions, has been
years in development. Milestones like these are important, and are
gratifying to the people who work on the mission.
“Now that Cheops has observed its first target, we are one step
closer to the start of the mission science,” said Kate Isaak, ESA Cheops
project scientist. “This beautifully blurred image carries the promise
of a new, deeper understanding of worlds beyond our Solar System.”
The Kepler mission revolutionized our understanding of exoplanets.
Its results confirmed what many had guessed: most stars host planets,
just like our Solar System does. Now, thanks largely to Kepler, we know
of over 4000 confirmed exoplanets. CHEOPS represents the next step in
characterizing and understanding exoplanets.
Preliminary looks at exoplanets were nowhere near as
precise as what CHEOPS will provide. Ground-based measurements can give
us a pretty good idea of an exoplanet’s mass. As a planet orbits its
star, it gives the star a little tug. From that tug, astronomers can
calculate the planet’s mass. But the planet’s density, and it’s
composition, are not revealed.
But the precise size measurements from CHEOPS, when combined with a
planet’s mass measurement, give us a much more accurate density, and
hence, composition. That’s how CHEOPS will advance exoplanet science.
“CHEOPS will take exoplanet science to a whole new level,” says Günther Hasinger, ESA Director of Science.
“After the discovery of thousands of planets, the quest can now turn
to characterization, investigating the physical and chemical properties
of many exoplanets and really getting to know what they are made of and
how they formed. CHEOPS will also pave the way for our future exoplanet
missions, from the international James Webb Telescope to ESA’s very own PLATO and ARIEL satellites, keeping European science at the forefront of exoplanet research.”
Artist’s
concept of Jupiter-sized exoplanet that orbits relatively close to its
star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech)The
CHEOPS mission will last about 3.5 years. 80% of that time will be
taken up by the CHEOPS Guaranteed Time Observing (GTO) program. Most of
the GTO program time will be used mostly to observe known exoplanets,
and to characterize them in more detail.
As Kepler
showed, exoplanets come in a wide variety of types, many of which are
very different from what we see in our Solar System. They include Hot
Jupiters, which are massive gas giants that orbit super close to their
star. There are tidally-locked planets with molten surfaces. There may
be ocean planets with no land area. And there are planets so close to
their star that the gravity warps them into an egg-like shape. CHEOPS
will grow our understanding of all of these types of planets we’re
finding. The planets it characterizes will likely be targets for further
study with even more powerful telescopes like the James Webb Space
Telescope.
The CHEOPS GTO will also look at exoplanets found with the radial
velocity method, and will observe their transits to find their sizes. It
will also look at other solar systems with multiple exoplanets, and try
to find any others that were missed.
Some
stars are known to host multiple exoplanets. Part of the CHEOPS mission
is to look at some of those solar systems and try to find other planets
that were missed. The three planets discovered in the L98-59 system by
NASA’s Transiting Exoplanet Survey Satellite (TESS) are compared to Mars
and Earth in order of increasing size in this illustration. Credit:
NASA’s Goddard Space Flight CenterThe other 20%
of CHEOPS’ time will be available to the astronomy community under the
Guest Observers (GO) program. Some of that time has already been
allotted to study some the Hot Jupiter HD 17156 b, the exoplanet DS Tuc Ab which TESS found, and the multi-planet system GJ 9827.
One of the planets orbiting GJ 9827 is the densest ever found, and may
be 50% iron, making it a very intriguing candidate for follow-up
observations.
CHEOPS’ science program should begin in April 2020, and will end around October 2023.
Yvonne Choquet-Bruhat, que acaba de cumplir 96 años, encontró solución al llamado problema de Cauchy para las ecuaciones de Einstein de vacío
La matemática francesa Yvonne Choquet-Bruhat, en una imagen tomada en 2006.RENATE SCHMID
El filósofo español José Ortega y Gasset afirmaba: “Sorprenderse, extrañarse… es comenzar a entender”. La misma idea empujó desde niña a Yvonne Choquet-Bruhat a querer “desentrañar alguno de los secretos del extraño universo en que vivimos, y del papel que los seres humanos jugamos en él”, como expresa en su autobiografía. La científica francesa, que el pasado 29 de diciembre cumplió 96 años, siempre ha confiado en que la física y las matemáticas nos podrían ayudar a llevar a cabo tal empeño. Sus contribuciones, enmarcadas fundamentalmente en el campo de la relatividad general, la han convertido en una destacada figura en el área de la física matemática del siglo XX.
Yvonne Choquet-Bruhat –el apellido “Choquet” lo adquirió en su segundo matrimonio con Gustave Choquet– nació en Lille (Francia) en el seno de una familia culta. Su padre, Georges Bruhat (1887-1945), fue profesor de física en la Universidad de Lillle, y su madre, Berthe Hubert (1892-1972), profesora de arte, literatura y filosofía en varios liceos franceses. Desde una temprana edad, Choquet-Bruhat mostró un gran talento para la física y las matemáticas. A los dieciocho años ganó una medalla de plata del “Concours General”, una competición a nivel nacional en la que se premiaba a los mejores estudiantes del país. En 1943 comenzó sus estudios de Matemáticas en la Escuela Normal Superior de Sévres, en las afueras de París, donde se graduó tres años más tarde.
Fue entonces cuando empezó su actividad investigadora en el prestigioso Centro Nacional de Investigación Científica francés (CNRS por sus siglas en francés), bajo el asesoramiento del reconocido físico matemático André Lichnerowicz. Realizó su tesis sobre el llamado problema de valor inicial (o problema de Cauchy) en el contexto de la relatividad general, en el que se estudia la existencia de soluciones para las ecuaciones planteadas por Albert Einstein, cuando éstas cumplen determinadas condiciones de partida. En el marco cosmológico, la cuestión determinaría si el futuro del universo está bien definido cuando sólo contamos con la información del mismo en un “tiempo concreto”, lo que se conoce como dato inicial del problema.
Choquet-Bruhat logró probar, mediante el estudio de complejas ecuaciones diferenciales y técnicas geométricas, que si se parte de un dato inicial que cumple ciertas restricciones físicas plausibles, hay únicamente un futuro posible para el universo
Choquet-Bruhat logró probar, mediante el estudio de complejas ecuaciones diferenciales y técnicas geométricas, que si se parte de un dato inicial que cumple ciertas restricciones físicas plausibles, hay únicamente un futuro posible para el universo. Su trabajo doctoral, que tiene por título “Théorème d’existence pour certains systèmes d’equations aux dérivées partielles non linéaires”, pone de manifiesto la naturaleza determinista de la teoría de Einstein, pues el futuro del universo queda fijado por la información que lo describe en un instante de tiempo.
En 1949 Choquet-Bruhat fue nombrada investigadora asistente del CNRS, y más tarde asociada. En 1951 aceptó un contrato postdoctoral en el Instituto de Estudios Avanzados de Princeton en EE UU Allí tuvo la oportunidad de conocer a Einstein, a quien pudo explicar en su despacho, con una combinación de francés e inglés, los principales logros de su tesis. El genio alemán la felicitó por el trabajo realizado y la invitó a visitarle a su despacho siempre que quisiera.
La solución al problema de Cauchy ha fundamentado, entre otros campos de investigación, el estudio de la estabilidad de las soluciones de las ecuaciones de Einstein, que analiza cuánto varían los universos que surgen de ligeras perturbaciones del dato inicial. ¿Se obtiene un universo ligeramente diferente al previsto, o por el contrario no tendría casi nada que ver con él? Por otra parte, este trabajo facilitó el uso técnicas numéricas y analíticas para aproximar las soluciones de las ecuaciones de Einstein, ya que habitualmente son muy difíciles de calcular de forma explícita. Aparte, más allá de su importancia dentro la teoría de la relatividad general, el trabajo de Choquet Bruhat ha establecido las bases para el estudio de otras teorías físicas como la hidrodinámica relativista, la teoría Gauge no abeliana o la supergravedad.
Entre otros méritos, destaca el haber sido la primera mujer elegida para formar parte de la Academia de las Ciencias Francesa
La fecunda trayectoria científica de la física matemática ha dado como fruto un total de siete libros y trescientos artículos, que la han hecho merecedora de importantes premios y galardones nacionales e internacionales. Entre otros méritos, destaca el haber sido la primera mujer elegida para formar parte de la Academia de las Ciencias Francesa, el 14 de mayo de 1979.
En las últimas líneas de su autobiografía, la científica francesa rememora una reflexión del filósofo Blaise Pascal, en la que éste admite tener “una tremenda ignorancia de todo”. A pesar de que Choquet-Bruhat reconozca la ingente cantidad de preguntas que quedan por responder, sus contribuciones han significado un avance científico considerable.
Después de una vida dedicada a la investigación, Yvonne Choquet-Bruhat ha podido ver cumplido el sueño de su infancia: aportar luz sobre algunos de los misterios del universo en que nos toca vivir.
Have you noticed that Orion the Hunter—one of the most iconic and familiar of the wintertime constellations—is looking a little… different as of late? The culprit is its upper shoulder star Alpha Orionis, aka Betelgeuse, which is looking markedly faint, the faintest it has been for the 21stcentury.
When will this nearby supernova candidate pop, and what would look like if it did?
The story starts, as all good astronomy and space stories seem to, on Friday night going into a holiday weekend. We started seeing discussion on Betelgeuse trending on social media on the evening of Friday, December 20th, and dug down to the source of the excitement: a December 8th paper on ‘The Fainting of the Nearby Red Supergiant Betelgeuse’ by researchers at Villanova University. Light curve estimates courtesy of the American Association of Variable Star Observers (AAVSO) verified the assertion that the star had indeed faded about one magnitude, or a little over one half from its usual magnitude +0.5 to +1.5. Noticing the sky was clear, we headed up to our parking garage rooftop observing site in downtown Norfolk, Virginia to take a look. Betelgeuse was indeed noticeably fainter, about a shade dimmer than nearby +1st magnitude Aldebaran.
Magnitude estimates of Betelgeuse, going back to 1970. Credit: The AAVSO.
Now, a change in one magnitude isn’t unusual for a variable star such as Betelgeuse… but such a large dip always gives the astronomical community pause. A red giant star 12 times as massive as our Sun and about 700 light years distant, the variability of red-orange Betelgeuse was first noted by astronomer Sir John Herschel in 1836. Physically, the star is currently bloated out to a radius of perhaps eight Astronomical Units (AU). If you plopped it down in the center of our solar system, Betelgeuse might extend all the way out to past the orbit of Jupiter.
Our (puny) host star, versus the neighbors, including Betelgeuse. Credit: Dave Dickinson
This fact also allowed astronomers to use the first crude optical interferometric measurements from the 2.5 meter telescope at Mount Wilson Observatory to measure Betelgeuse’s physical diameter of 50 milliarcseconds. In the late 1980s, astronomers used in emerging technique of aperture masking interferometry to obtain the first direct ‘image’ of Betelgeuse.
A pulsating Betelgeuse in the ultraviolet. Credit: NASA/HST
Betelgeuse is always worth keeping an eye on, as it’s one of the closest candidates in our galaxy for a nearby supernova. We see supernovae frequently in distant galaxies, but such an event has not been witnessed in our galaxy in the telescopic era: Kepler’s Star in 1604 in the constellation Ophiuchus was the last supernova observed in the Milky Way, though a supernova in the nearby Large Magellanic Cloud put on a good show in 1987. A red giant like Betelgeuse lives fast and dies young, exhausting its supply of hydrogen fuel in just under 10 million years. The star is destined to undergo a core implosion and massive collapse and rebound as a Type II supernova. Such an explosion could occur 100,000 years from now… or tonight.
Still fading… our brief smartphone capture of Betelgeuse and Orion from Virginia Beach on Christmas Day 2019. Credit Dave Dickinson
Is the fading act a prelude to a truly spectacular show, or a false alarm? Astronomers are unsure, but a supernova event just 700-odd light-years away would be an unrepresented opportunity to study one up close. Not only would every optical telescope get trained on the exploding star, but assets such as the Laser Interferometry Gravitational Wave Observatory (LIGO) could detect gravitational waves from a nearby supernova, and neutrino observatories such as Ice Cube buried in the Antarctic ice could detect the event as well.
…and fortunately for us, we’re safely out of the 50 light-year ‘kill zone’ for receiving any inbound lethal radiation from Betelgeuse: a supernova would simply be a scientifically interesting event, and put on a good show. Ancient supernovae may have had a hand in the evolution of life on Earth, and a recent study suggests that one might even have forced early humans to walk upright. Here’s the rogues gallery list of stars that are current nearby supernovae candidates:
Nearby supernova candidates out to 1,000 light-years. Credit: Dave Dickinson
What would a supernova in Orion look like? Well, using the last supernova in the Large Magellanic Cloud (also a Type IIb event) as a guide, we calculate that when it does blow, Betelgeuse would shine at magnitude -10. That’s 16 times fainter than a Full Moon, but 100 times brighter than Venus, making it easily visible in the daytime sky. A Betelgeuse-gone-supernova would also easily cast noticeable nighttime shadows.
But see the ongoing fading event for yourself. Betelgeuse is easy to find in December, rising to the east at dusk. In fact, northern hemisphere winter is the very best time for the star to blow, as it’s roughly opposite to the Sun, and would dominate the night sky. Summer would be the worst time, as it would tease us from beyond the far side with the Sun in the daytime sky.
You can even guesstimate Betelgeuse’s brightness yourself, using the nearby stars of the Winter Hexagon asterism as a guide:
Betelgeuse, versus the stars of the Winter Hexagon with annotated magnitudes (note: this was taken prior to the current dimming event). Image credit and copyright: Steve Brown.
What’s next? Well, expect Betelgeuse to brighten again in early 2020… though if it rebounds into negative magnitude territory past Rigel and Sirius, well, then things could get really exciting.
For now though, we’re in a wait-and-see-mode for any New Year’s Eve fireworks from Betelgeuse. Such an occurrence would be bittersweet: we would be extraordinarily lucky to see Betelgeuse go supernova in our lifetime… but familiar Orion the Hunter would never look the same again.
Lead image: Orion with a fading Betelgeuse from December 21st, 2019 courtesy of Alan Dyer.
Dos telescopios de Canarias aclaran cómo suceden las mayores explosiones del cosmos
Las dos antenas de MAGIC, durante la lluvia de Perseidas en 2016.DANIEL LÓPEZ
El 14 de enero laastrofísicaElena Moretti recibió una llamada que no olvidará fácilmente. “¿Esta señal que estamos viendo es un simulacro?”, dijeron al otro lado del teléfono. Era de noche cerrada en el Observatorio del Roque de los Muchachos, una cima de origen volcánico en la isla de La Palma ideal para laobservación astronómica. La científica saltó de la cama y en dos minutos estaba frente a las pantallas del centro de control. No era un simulacro: los dostelescopiosMAGIC habían captado claramente un grupo de fotones —partículas de luz— que era unas 100 veces más potentes que cualquier otro detectado antes.
“Aunque lo veía delante de mis ojos no podía creerlo”, explica Moretti. Todo había comenzado tres minutos antes de las nueve de la noche, cuando dos telescopios espaciales, Swift y Fermi, detectaron un potente estallido de rayos gamma. En unos 20 segundos enviaron una alerta a la Tierra. De forma totalmente automática, las dos imponentes antenas de 64 toneladas de los telescopios MAGIC giraron sobre sí mismas 35 segundos después para apuntar justo al punto del cielo desde el que llegaba la señal, que duró unos 30 minutos.
“Esa noche nos quedamos trabajando unas cuatro horas más. La señal fue debilitándose y después desapareció detrás del horizonte. Enviamos una nota de alerta al resto de la comunidad astrofísica internacional para que intentaran seguir observándola”, recuerda la astrofísica, que trabaja en el Instituto de Física de Altas Energías, en Barcelona.
Los resultados de las observaciones de los MAGIC y de muchos otros observatorios espaciales y terrestres se publican este miércoles en la prestigiosa revista científica Nature. Dos estudios confirman que los MAGIC han sido los primeros en captar el grupo de fotones con más energía que se han observado después de un estallido de rayos gamma. Estas son las mayores explosiones del universo actual, capaces de liberar en apenas 100 segundos la misma energía que emitirá el Sol en lo que le queda de vida (unos 10.000 millones de años).
Los telescopios MAGIC, en el Observatorio del Roque de los Muchachos de la isla de La Palma.ALICIA LÓPEZ-ORAMAS
Los fotones registrados tienen una energía media de un teraelectronvoltio, un billón de veces más que los fotones convencionales que podemos ver los humanos. “Esta es la luz más potente que se ha captado teniendo en cuenta la cantidad de energía liberada y el tiempo que duró el estallido”, explica Moretti. “En el universo conocemos otras fuentes capaces de emitir luz así de potente, como los núcleos de galaxias activos [agujeros negros], pero tardan miles de millones de años en hacerlo”, destaca.
Esta detección aclara la física de las emisiones de rayos gamma y demuestra por primera vez que pueden alcanzar mucha más energía de lo que se pensaba. “Durante 20 años hemos estado recibiendo señales de fuentes de rayos gamma, unas 110 en total, pero nunca habíamos visto algo tan escandaloso, tan impresionante”, resalta María Victoria Fonseca, astrofísica de la Universidad Complutense de Madrid que trabaja en MAGIC —siglas inglesas de Telescopio de Rayos Gamma por Emisión de Radiación Cherenkov en la Atmósfera— desde que sus telescopios comenzaron a funcionar en 2004.
Tras la explosión estelar se generaron dos potentes haces de rayos gamma y rayos x que salieron disparados en direcciones opuestas. Después de esta fase de emisión rápida, la metralla escupida por el astro generó una onda de choque que comprimió el medio interestelar formando plasma y un intenso campo magnético en el que los electrones quedaron atrapados en una trayectoria circular hasta alcanzar altas energías y velocidades cercanas a la de la luz. Es el fenómeno conocido como sincrotrón en el que se basan los aceleradores de partículas que, en la Tierra, permiten hacer imagen médica por rayos x o penetrar en la materia sin dañarla para descubrir pinturas ocultas en lienzos de Picasso, Van Gogh o Degas.
En 1923, el físico estadounidense Arthur Compton descubrió que un fotón podía chocar con un electrón y pasarle parte de su energía, el efecto Compton que le valió el Nobel de física en 1927. Los investigadores de MAGIC creen que lo que han observado es el efecto inverso de Compton en el que son los electrones acelerados los que ceden parte de su energía a los fotones hasta que estos rompen la barrera de los teraelectronvoltios. Es una posibilidad predicha por la teoría pero nunca confirmada hasta ahora.
"¿Por qué hemos tardado tantos años en detectar este fenómeno?”, se pregunta Bing Zhang, físico de la Universidad de Nevada (EE UU), en una opinión publicada junto a los artículos. Aunque se piensa que hay un estallido de rayos gamma al día, solo son detectables a estas energías los que son muy potentes y suceden relativamente cerca de la Tierra. Además, tiene que ser de noche y es necesario que haga buen tiempo y que la luz llegue a una zona donde haya telescopios. El físico explica que la detección de este tipo de luz se hará “rutinaria” en poco tiempo gracias al trabajo de detectores como el HAWC, en la ladera del volcán Sierra Negra (México), o la red de Telescopios Cherenkov, en La Palma y en Chile, y el observatorio de Daocheng, en China.
