'Symbiotic stars' caught snacking on each other outside the Milky Way

For the first time, stars snacking on their stellar neighbors outside the Milky Way have had their orbits fully mapped. Using the Sloan Digital Sky Survey, astronomers have identified two pairs of stars beyond the galaxy that are consuming their companions. The new discovery can help astronomers understand if distant galactic environments function similarly to or differently from the Milky Way. It can also provide insight into one of the fundamental methods of measuring distance in the night sky. More than half the stars in the Milky Way come in pairs. While it seems likely that binary stars should make up a significant fraction of other galaxies, scientists have been unable to confirm that because at such large distances ordinary stars are too faint to see.But so-called symbiotic stars, where one companion consumes the other, can be extremely bright, making them easier to observe. "Measuring the orbits of these symbiotic star systems is an important step towards learning whether other galaxies create binary stars like those in the Milky Way," Jasmin Washington, a co-author of the new study and a graduate student at the University of Arizona, said in a statement. She was an undergraduate at the University of Virginia during the project. Washington and her fellow author, Hannah Lewis, a graduate student at the University of Virginia, presented the results on Tuesday (Jan 12) at the 237th meeting of the American Astronomical Society, held virtually last week.

An artistic impression of the Draco C1 symbiotic binary star system showing material flowing off the red giant star onto its white dwarf companion.

(Image: © John Blondin/North Carolina State University)

"We have developed for the first time ever the complete understanding of the architecture of an extragalactic [symbiotic] system," Washington said at the briefing.

Serendipitous snackers

Although a pair of stars may be born together, they can age differently due to their masses. The more massive of the two will quickly burn through its material to reach the end of its lifetime first. If that star is large enough, it will leave behind a compact white dwarf. Although small and dim, white dwarfs can pack the mass of the sun into an object the size of the Earth. If close enough, the gravity of the dense objects can pull material from their companion, creating a signal that astronomers can identify from extremely far away. While astronomers know that stellar pairs are common in the Milky Way, they remain uncertain how large a fraction they make up in other galaxies.

"The properties of binary systems likely depend on the environment that they formed in," Lewis said at the briefing. "Those environmental properties can vary vastly between galaxies."

For the last decade, Sloan Telescope’s Apache Point Observatory Galactic Evolution Explorer (APOGEE) survey has studied the sky, gathering data about hundreds of thousands of stars in the Milky Way and its nearest galactic neighbors. These include the Draco dwarf spheroidal galaxy and the Small Magellanic Cloud (SMC), roughly 260,000 and 200,000 light-years respectively.

"These two galaxies alone show how conditions can vary wildly between systems," Lewis said. Draco is an ancient galaxy, a hundred thousand times smaller than the Milky Way, and is dominated by dark matter rather than stars. The SMC is younger and larger, only 200 times smaller than our galaxy and composed of old and young stars. Both galaxies are home to a symbiotic stellar pair visible to APOGEE, the Draco C1 and LIN 358 pair, respectively.

This graph shows the motions measured by the APOGEE data for the Draco C1 symbiotic binary star system, which has been monitored repeatedly over the last five years. Black dots represent the data, while the blue curve shows the computer model for the orbit of the red giant as it circles the white dwarf, moving toward and away from the observer. (Image credit: Washington et al.)

Slurping material from the neighboring stars only allows astronomers to identify the pair. The Doppler shift — the same phenomena responsible for causing train whistles to reach a higher pitch as they move closer and lower as they move farther away — also causes changes in the frequency of light coming from a star, depending on whether it is moving closer to or farther from the observer. That back-and-forth motion can help astronomers to calculate the full orbit of the binary system and the masses of both stars.

By combing through several years of APOGEE data, Washington realized that the stars in Draco C1 take roughly three Earth years to orbit one another, while LIN 358's components take just over two. The results reveal the first full orbital measurements of any symbiotic star system outside the Milky Way.

"Very few symbiotic stars have ever been monitored long enough for astronomers to watch the full willing dance," Lewis said in a statement. "And no one has ever done this in detail for symbiotic stars in other galaxies."

The new measurements will help astronomers better understand star formation in other galaxies.

"Dwarf galaxies have very different internal environments and evolutionary histories from the Milky Way," Borja Anguiano, also at the University of Virginia, said in the statement. A co-author on the paper, Anguiano originally discovered that APOGEE had serendipitously observed Draco C1 and LIN 358 several times.

"Soon we will have enough orbits mapped for binaries in other galaxies that we may begin to answer the question of whether different types of galaxies are more efficient at making binary stars."

The results from the observations of Draco C1 were published earlier this year in the Astrophysical Journal Letters.

Standard candles

In some symbiotic stars, the white dwarf can slurp enough material from its companion that it explodes in a Type Ia supernova. These extremely bright blasts can be seen across the universe, and they all start out with the same brightness for a nearby observer. Astronomers can use the apparent brightness of the supernova to calculate its distance, making Type Ia supernovas a "standard candle" for measuring the universe.

While Draco C1 and LIN 358 are unlikely to explode as supernovae anytime soon, understanding how they work can provide insights into how these standard candles evolve.

"Because we rely on Type Ia supernovae as distance measurements, it's important that we understand exactly how they work, and what systems we should be looking for as possible supernovae progenitors," Anguiano said. "Being able to study the orbits of symbiotic stars in other galaxies will allow us to confirm whether the process of forming Type Ia supernovae is universal."

Mapping the orbital characteristics of Draco C1 and LIN 358 is a "first incredible step" towards using a decade's worth of APOGEE data to understand binary stars outside the Milky Way, Washington said at the briefing.

"Studying extragalactic symbiotic stars in great detail and being able to precisely derive their orbits and stellar parameters could provide important insights into these cosmic markers," she said.

Back to Venus armed with laboratory findings

Venus's impenetrable atmosphere has long made it difficult to conduct a thorough investigation of our neighbouring planet. In a step forward, by conducting laboratory experiments scientists from the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) have now developed a way of determining the nature of the planet's surface using new instruments from orbit. The entire surface of Venus can now be mapped mineralogically for the first time, addressing a large gap in planetary research. Venus is Earth's sister planet. It is almost exactly the same size and orbits on average only 40 million kilometres closer to the Sun. However, the two planets developed in very different ways. On Earth, continents formed, separated by oceans. Then some three and a half billion years ago, life emerged under its atmosphere and evolved into the vast variety of organisms that we know today. Things happened very differently on Venus, which is surrounded by an atmosphere of gas a hundred times thicker than that of Earth. Within it, the extreme greenhouse effect results in a constant surface temperature of 470 degrees Celsius - a temperature at which water would instantly evaporate and even lead would melt. The planet is permanently enveloped in thick clouds of sulphuric acid, making it impossible for telescopes on Earth or instruments on board spacecraft to acquire even a glimpse of the surface. Scientists have managed, however, to map its landscape using radar. And now, through a series of laboratory experiments, DLR researchers have developed a new method for determining the nature of the planet's surface from orbit.

"For a good ten years, we have been using a unique laboratory facility to measure the emission properties of various rocks of the kind we might expect to find on Venus under the same extreme conditions that prevail on the planet," says Jorn Helbert, Head of DLR's Planetary Spectroscopy Laboratory (PSL) and lead author of a research paper that has now been published in Science Advances magazine. "The reflectance and emissivity of rocks change when they are exposed to the high temperatures that you find on Venus. As a result, spectral profiles measured at terrestrial temperatures cannot simply be applied there. But now, we have a tool that we can use as the basis for new instruments on the next planned missions to Venus that will finally allow us to determine which types of rock exist there."

Concordance with existing surface measurements from Venus
The four-person research group made up of researchers from DLR, the Planetary Science Institute in Tucson, Arizona, and Mount Holyoke College in Massachusetts have used the results of their laboratory experiments to devise a new 'spectral library' for various types of rock. "Determining the emission spectra in this way has enabled us to reconstruct the iron oxide content at the landing site of the Soviet Union's Venera 9 and Venera 10 landers for the very first time," says DLR Planetary Scientist Alessandro Maturilli. "In 1975, the two landers transmitted images from Venus and provided important measurements. However, they were not equipped with an instrument that could directly measure iron oxide content."

The two landers provided the only direct spectral measurements of Venusian rocks. The emission profiles determined in the laboratory and the spectra determined by the Venera missions are in very good agreement. "As such, we have demonstrated the accuracy of our new method, which represents a big step forward," says Jorn Helbert. Although further Venus lander missions are currently under discussion, global mapping of the planet can only be conducted from orbit. However, the atmosphere of Venus is impenetrable to wavelengths of visible light - those that the human eye can see. To make mapping of the surface possible despite the planet's atmosphere, scientists are focusing on what are known as 'atmospheric windows'. These are narrow bands of wavelengths at which the atmosphere of Venus is transparent, and thus allow a view of the surface. Five such 'windows' exist at wavelengths close to 1000 nanometres (one micrometre). These wavelengths are in the near-infrared, which is adjacent to the visible portion of the electromagnetic spectrum (approximately 400-700 nanometres).

Venus returns to the focus of planetary research
Through their experiment, the researchers have shown that for rock types measured in the laboratory, the spectra and their characteristic profiles can be used to reliably identify them from orbit. "Our aim is now to create the first global map of rocks on Venus," says Helbert. "That would be a major achievement! After all, we know far too little about Venus. In its infancy, the planet may have had water, like Earth, and may also have been less hostile to life." The scientists are looking to use the Venus Emissivity Mapper (VEM) instrument to implement their plan, mapping emissions in the few atmospheric windows available at near-infrared wavelengths. VEM could be installed on the EnVision mission of the European Space Agency (ESA) and on NASA's VERITAS orbiter later this decade.

Venus, Earth's celestial neighbour and often described as its sister planet, was the first target for interplanetary spacecraft. The Soviet mission Venera 1 launched in 1961 and the American Mariner 2 in 1962. Despite a number of spectacular successes, particularly the Soviet space programme's initial orbiters and then eight landings between 1970 and 1983, the planet named after the Roman goddess of love later fell somewhat out of favour in planetary research. Between 1990 and 1994, NASA's Magellan orbiter mapped Venus using radar, revealing myriad details of its multifaceted surface in high-resolution. From 2006 to 2015, ESA's Venus Express mission investigated the planet across a series of seven experiments.

However, we still know little about the nature of the planet's surface. For Earth's other immediate neighbours, the Moon and Mars, determining rock types, mineralogical composition and the abundance of chemical elements was far easier. As a result, nowadays we have a fairly thorough understanding of them. The astronauts involved in the Apollo missions and the robotic missions of the Soviet Union returned 400 kilograms of sample material from the Moon to Earth. Half a dozen landers have been able to analyse the rocks on Mars. A landing on Venus would be a heroic feat, as the lander descends into an increasingly hot oven. The high temperatures and atmospheric pressure - which reaches 92 bar on the ground (equivalent to the pressure at 900 metres underwater on Earth) - would put the electronics under immense strain. The Venera 13 lander was able to withstand these conditions for the greatest amount of time so far and, on 30 October 1981, succeeded in transmitting data from the furnace-like surface of Venus for almost two hours. The new method developed in this laboratory study would allow the surface of Venus to be studied systematically from orbit over a period of many years, without having to run the risk of a landing.

NASA to Host Virtual Briefing on February Perseverance Mars Rover Landing

NASA is hosting a media briefing on Wednesday, Jan. 27, at 4:30 p.m. EST to discuss the upcoming landing of the Mars 2020 Perseverance rover. The event will air live on NASA TV, the agency's website, and YouTube. Perseverance lands Feb. 18, carrying new science instruments and technologies, including the Ingenuity Mars Helicopter on its belly. Perseverance will use a drill on the end of its robotic arm to capture rock and regolith (broken rock and dust) samples in metal tubes, which will be deposited on the surface of Mars for a future mission to collect and return to Earth. The rover will seek signs of ancient life on the Red Planet as a primary goal.

Perseverance was built and managed for NASA by the agency's Jet Propulsion Laboratory in Southern California.

Participating in the briefing are:


Thomas Zurbuchen, associate administrator, Science Mission Directorate, NASA Headquarters
Lori Glaze, director, Planetary Science Division, NASA Headquarters
Matt Wallace, Mars 2020 deputy project manager, JPL
Allen Chen, Mars 2020 entry, descent, and landing lead, JPL
Ken Farley, Mars 2020 project scientist, Caltech
Briony Horgan, Mars 2020 science team member, Purdue University


Media who would like to ask questions via phone during the event must provide their name and affiliation by noon EST Tuesday, Jan. 26, to Rexana Vizza at rexana.v.vizza@jpl.nasa.gov.

Media and the public also may ask questions on social media during the briefing using #CountdownToMars.

To learn more about Perseverance, visit:

https://nasa.gov/perseverance

 and

https://mars.nasa.gov/mars2020/

Citizen scientists help create 3D map of local stellar neighborhood

Is our solar system located in a typical Milky Way neighborhood? Scientists have gotten closer to answering this question, thanks to the NASA-funded Backyard Worlds: Planet 9 project, a "citizen science" collaboration between professional scientists and members of the public. Scientists tapped into the worldwide network of 150,000 volunteers using Backyard Worlds: Planet 9 to find new examples of brown dwarfs. These objects are balls of gas that are not heavy enough to be stars, since they can't power themselves through nuclear fusion the way stars do. And while "brown" is in the name, they would appear magenta or orange-red if a person could see them close up. By making a complete map of these objects, scientists could find out whether different kinds of brown dwarfs are evenly distributed in our solar system's neighborhood. Telescopes can detect brown dwarfs because they emit heat, in the form of infrared light, left over from their formation. Infrared light is invisible to human eyes, but it can reveal tantalizing details about brown dwarfs and other objects throughout the universe. The result of the new citizen science effort is the most complete map to date of L, T and Y dwarfs in the vicinity of the solar system. These brown dwarf varieties can have temperatures of up to thousands of degrees Fahrenheit, but the Y dwarfs, which are the coolest, may have below-freezing temperatures and clouds made of water.

This image shows Earth surrounded by the nearest brown dwarfs, shown in red, against the backdrop of surrounding constellations.


Of course, an astronomer's idea of a neighborhood is different in space than on Earth. The map encompasses a radius of 65 light-years, or about 400 trillion miles, with "close neighbors" inhabiting space within about 35 light-years, or 200 trillion miles.

Since 2017, citizen scientists have been searching for brown dwarf candidates as part of Backyard Worlds, using data from NASA's Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) satellite along with all-sky observations collected between 2010 and 2011 under its previous moniker, WISE. The Backyard Worlds team also collaborated with Caltech's Summer Research Connection program to involve high school students in finding brown dwarfs. Both worldwide volunteers and high school students in the Pasadena, California, area are listed as co-authors of the study, which was presented at the 237th meeting of the American Astronomical Society.

While brown dwarfs are millions to billions of years old, this team of professional and citizen scientists had a much shorter deadline to find them. They knew that NASA's Spitzer Space Telescope was the only operating observatory that could confirm the distances and positions of the brown dwarfs they were interested in, and Spitzer was set to retire in January 2020. It was a frantic rush to find as many brown dwarfs as they could so Spitzer could reveal their locations more precisely.

Fortunately, citizen scientists helped save the day - they discovered dozens of new brown dwarfs.

"Without the citizen scientists, we couldn't have created such a complete sample in so short a time," said J. Davy Kirkpatrick, scientist at Caltech/IPAC in Pasadena and lead author of the study. "Having the power of thousands of inquiring eyes on the data enabled us to find brown dwarf candidates much faster."

Professional astronomers then used Spitzer to observe 361 local brown dwarfs of types L, T, and Y, and combined them with previous discoveries to make a 3D map of 525 brown dwarfs. Besides the citizen science discoveries, scientists made use of CatWise, a NASA-funded catalog of objects from WISE and NEOWISE, to complete their census.

And there's a surprise: One of our solar system's neighbors - the galaxy's coldest known Y dwarf, with temperatures likely below freezing - represents a rare resident in the cosmic neighborhood. Astronomers would have expected to find a lot more of them in the vicinity. But this may be because current telescopes aren't sensitive enough to find them, since these objects are so faint.

As previous research has found, of the seven objects nearest to our solar system, three are rare types of brown dwarfs. The rest are normal stars: red dwarfs Proxima Centauri and Barnard's Star, and Sun-like stars Alpha Centauri A and B.

"If you were to put the Sun at a random place within our 3D map and you were to ask, 'Typically, what do its neighbors look like?' We find that they would look very different from what our actual neighbors are," said Aaron Meisner, assistant scientist at the National Science Foundation's NOIRLab and co-author of the study.

So, is the Sun in an unusually diverse cosmic neighborhood, or is it just that nearby Y dwarfs are easiest to spot? Astronomers will need to investigate further to find out.

Some of these L, T, and Y dwarfs have masses and temperatures similar to exoplanets - planets beyond our solar system. Getting details about distant planets can be challenging because if they orbit other stars, starlight is a lot brighter than the planet. Since brown dwarfs in this study do not orbit stars, a telescope does not have to subtract starlight to look at them. This makes brown dwarfs a new kind of laboratory for understanding exoplanets.

Scientists will learn even more about brown dwarfs with NASA's forthcoming James Webb Space Telescope, which will examine these mysterious objects in detail in infrared light. NASA's upcoming SPHEREx mission, which will be an all-sky infrared survey, also presents new opportunities to characterize more brown dwarfs.

The Backyard Worlds: Planet 9 project is ongoing and open to anyone worldwide who wants to join the quest to find more mysterious objects in spacecraft data. In addition to a total of about 3,000 brown dwarfs, volunteers have helped find the oldest, coldest white dwarf surrounded by a disk of debris.

"I enjoy this project because the objects that we send to the researchers might get observed with a big telescope," said Melina Thevenot, a citizen scientist in Germany who is listed as a co-author of the new study. "I think we volunteers can really see the fruits of our efforts with this project and the publications by the science team."

New solar arrays to power International Space Station Research

As the International Space Station orbits Earth, its four pairs of solar arrays soak up the sun's energy to provide electrical power for the numerous research and science investigations conducted every day, as well as the continued operations of the orbiting platform. The space station is the springboard to NASA's Artemis missions to the Moon, a platform to test advanced technologies for human exploration of deep space and future mission to Mars. NASA also has opened the space station for business and commercial activities, including private astronauts missions. Designed for a 15-year service life, the solar arrays have been operating continuously since the first pair was deployed in December 2000, with additional array pairs delivered in September 2006, June 2007, and March 2009. The first pair of solar arrays has now provided continuous electrical power to the station for more than 20 years as more modules were added and dozens of crews tackled thousands of scientific experiments and continued operations through hundreds of spacewalks, cargo missions, and more. Though they are functioning well, the current solar arrays are showing signs of degradation, as expected. To ensure a sufficient power supply is maintained for NASA's exploration technology demonstrations for Artemis and beyond as well as utilization and commercialization, NASA will be augmenting six of the eight existing power channels of the space station with new solar arrays.

Boeing, NASA's prime contractor for space station operations, its subsidiary Spectrolab, and major supplier Deployable Space Systems (DSS) will provide the new arrays. The combination of the eight original, larger arrays, and the smaller, more efficient new arrays will restore the power generation of each augmented array to approximately the amount generated when the original arrays were first installed, providing a 20% to 30% increase in power for space station research and operations.

The new solar arrays will be a larger version of the Roll-Out Solar Array (ROSA) technology that successfully demonstrated the mechanical capabilities of solar array deployment during its test on the space station in June 2017.

The new solar arrays will be positioned in front of six of the current arrays, and will use the existing sun tracking, power distribution, and channelization. This approach is similar to the one used to upgrade the station's external television cameras to high definition, using the existing power and control mechanisms.

The new arrays will shade slightly over half of the length of the existing arrays and will be connected to the same power system to augment the existing supply. The eight current arrays are currently capable of generating up to 160 kilowatts of power during orbital daytime, about half of which is stored in the station's batteries for use while the station is not in sunlight. Each new solar array will produce more than 20 kilowatts of electricity, eventually totaling 120 kilowatts (120,000 watts) of augmented power during orbital daytime.

In addition, the remaining uncovered solar array pair and partially uncovered original arrays will continue to generate approximately 95 kilowatts of power for a total of up to 215 kilowatts (215,000 watts) of power available to support station operations at completion. For comparison, an active computer and monitor may use up to 270 watts, and a small refrigerator uses about 725 watts.

The solar arrays will be delivered to the International Space Station in pairs in the unpressurized trunk of the SpaceX Dragon cargo spacecraft during three resupply missions starting in 2021, when the second pair of current arrays reaches the 15th year of its design life. The installation of each solar array will require two spacewalks: one to prepare the worksite with a modification kit and another to install the new solar array.

NASA signed a modification to the ISS Vehicle Sustaining Engineering contract with Boeing to provide the six new solar arrays. Doing so provides the International Space Station with enough power to maintain normal operations and ensure adequate power for future opportunities in low-Earth orbit, whether for NASA and its international partners or commercial companies.