Beyond the brim, Sombrero Galaxy's halo suggests turbulent past

by Claire Andreoli / Rob Gutro, NASA's Goddard Space Flight Center







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

NASA's Hubble surveys gigantic galaxy

by ESA/Hubble Information Centre

 

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

Here are the First Pictures from CHEOPS

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.

Artist’s impression of CHEOPS © ESA / ATG medialab

Even though it’s blurry, it’s the first image. And that makes it a milestone for the ESA and the CHEOPS team.
“This is a defining moment for the mission,” said Nicola Rando, ESA project manager for Cheops, in a press release.
“To the engineers and scientists across Europe who have worked and continue to work on Cheops, this image represents the culmination of many years of dedication and effort – designing, planning, coordinating and building this new and unique satellite,” said Rando.

“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 Center

The 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.

More:

• Press Release: CHEOPS space telescope takes its first pictures
• Press Release: A perfect blur – First image by exoplanet watcher Cheops
• Universe Today: ESA’s CHEOPS Just Launched. We’re About to Learn a LOT More About Exoplanets 

 Fuente: https://www.universetoday.com/144967/here-are-the-first-pictures-from-cheops/