Inouye Solar Telescope releases first image of a sunspot

ASSOCIATION OF UNIVERSITIES FOR RESEARCH IN ASTRONOMY (AURA)

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VIDEO: THE WAVE FRONT CORRECTION CONTEXT VIEWER CAMERA AT THE NSF'S INOUYE SOLAR TELESCOPE RECORDED THIS MOVIE OF A SUNSPOT ON JAN. 28, 2020. THE 2000 BY 2000-PIXEL CAMERA CAPTURED THIS... view more 

CREDIT: NSF/NSO/AURA

The world's largest solar observatory, the U.S. National Science Foundation's Daniel K. Inouye Solar Telescope, just released its first image of a sunspot. Although the telescope is still in the final phases of completion, the image is an indication of how the telescope's advanced optics and four-meter primary mirror will give scientists the best view of the Sun from Earth throughout the next solar cycle.

The image, taken January 28, 2020, is not the same naked eye sunspot currently visible on the Sun. This sunspot image accompanies a new paper by Dr. Thomas Rimmele and his team. Rimmele is the associate director at NSF's National Solar Observatory (NSO), the organization responsible for building and operating the Inouye Solar Telescope. The paper is the first in a series of Inouye-related articles featured in Solar Physics. The paper details the optics, mechanical systems, instruments, operational plans and scientific objectives of the Inouye Solar Telescope. Solar Physics will publish the remaining papers in early 2021.

Read Daniel K. Inouye Solar Telescope - Observatory Overview, by Thomas R. Rimmele et al. - Solar Physics volume 295, issue 12, 2020

"The sunspot image achieves a spatial resolution about 2.5 times higher than ever previously achieved, showing magnetic structures as small as 20 kilometers on the surface of the sun," said Rimmele.

The image reveals striking details of the sunspot's structure as seen at the Sun's surface. The streaky appearance of hot and cool gas spidering out from the darker center is the result of sculpting by a convergence of intense magnetic fields and hot gasses boiling up from below.

The concentration of magnetic fields in this dark region suppresses heat within the Sun from reaching the surface. Although the dark area of the sunspot is cooler than the surrounding area of the Sun, it is still extremely hot with a temperature of more than 7,500 degrees Fahrenheit.

This sunspot image, measuring about 10,000 miles across, is just a tiny part of the Sun. However, the sunspot is large enough that Earth could comfortably fit inside.

CAPTION

This is the first sunspot image taken on Jan. 28, 2020, by the NSF's Inouye Solar Telescope's Wave Front Correction context viewer. The image reveals striking details of the sunspot's structure as seen at the sun's surface. The sunspot is sculpted by a convergence of intense magnetic fields and hot gas boiling up from below. This image uses a warm palette of red and orange, but the context viewer took this sunspot image at the wavelength of 530 nanometers -- in the greenish-yellow part of the visible spectrum. This is not the same naked eye sunspot group visible on the sun in late November and early December 2020.

CREDIT

NSO/AURA/NSF

Sunspots are the most visible representation of solar activity. Scientists know that the more sunspots that are visible on the Sun, the more active the Sun is. The Sun reached solar minimum, the time of fewest sunspots during its 11-year solar cycle, in December 2019. This sunspot was one of the first of the new solar cycle. Solar maximum for the current solar cycle is predicted in mid-2025.

"With this solar cycle just beginning, we also enter the era of the Inouye Solar Telescope," says Dr. Matt Mountain, president of the Association of Universities for Research in Astronomy (AURA), the organization that manages NSO and the Inouye Solar Telescope. "We can now point the world's most advanced solar telescope at the Sun to capture and share incredibly detailed images and add to our scientific insights about the Sun's activity."

Sunspots, and associated solar flares and coronal mass ejections, cause many space weather events, which frequently impact the Earth, a consequence of living inside the extended atmosphere of a star. These events affect technological life on Earth. The magnetic fields associated with solar storms can impact power grids, communications, GPS navigation, air travel, satellites and humans living in space. The Inouye Solar Telescope is poised to add important capabilities to the complement of tools optimized to study solar activity particularly magnetic fields.

NSF's Inouye Solar Telescope is located on the island of Maui in Hawaii. Construction began in 2013 and is slated to be completed in 2021.

"While the start of telescope operations has been slightly delayed due to the impacts of the COVID-19 global pandemic," said Dr. David Boboltz, NSF Program Director for the Inouye Solar Telescope, "this image represents an early preview of the unprecedented capabilities that the facility will bring to bear on our understanding of the Sun."

The Daniel K. Inouye Solar Telescope is a facility of the National Science Foundation operated by the National Solar Observatory under a cooperative agreement with the Association of Universities for Research in Astronomy, Inc. The Inouye Solar Telescope is located on land of spiritual and cultural significance to Native Hawaiian people. The use of this important site to further scientific knowledge is done so with appreciation and respect.

CAPTION

The National Science Foundation's Inouye Solar Telescope.

CREDIT

NSF/NSO/AURA

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Image Use:

The images and movies shown here are part of the facility Science Verification Phase. They are for the sole purpose of promotion and are not released for scientific use. Science Verification Phase data is proprietary to the Inouye Solar Telescope project, and its use for publications or outreach purposes requires approval by the NSO Director, and notification to the cognizant NSF program officer. Please contact outreach@nso.edu for details and questions. The original data are still being processed and are not fully calibrated for scientific use. Images have been processed to remove noise and enhance the visibility (contrast) of small-scale (magnetic) features while maintaining their shape. The movie frames have been smoothed to remove noise.

This product is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0). For image use conditions, please visit our image use page or email outreach@nso.edu.

Contacts:

Claire Raftery
Head of Communications
National Solar Observatory
303-735-9044
claire@nso.edu
National Science Foundation
media@nsf.gov

Rochester researchers uncover key clues about the solar system's history

New clues lead to a better understanding of the evolution of the solar system and the origin of Earth as a habitable planet

UNIVERSITY OF ROCHESTER

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IMAGE: ILLUSTRATION OF SOLAR WIND FLOWING OVER ASTEROIDS IN THE EARLY SOLAR SYSTEM. THE MAGNETIC FIELD OF THE SOLAR WIND (WHITE LINE/ARROWS) MAGNETIZES THE ASTEROID (RED ARROW). RESEARCHERS AT THE UNIVERSITY... view more 

CREDIT: UNIVERSITY OF ROCHESTER ILLUSTRATION / MICHAEL OSADCIW

In a new paper published in the journal Nature Communications Earth and Environment, researchers at the University of Rochester were able to use magnetism to determine, for the first time, when carbonaceous chondrite asteroids--asteroids that are rich in water and amino acids--first arrived in the inner solar system. The research provides data that helps inform scientists about the early origins of the solar system and why some planets, such as Earth, became habitable and were able to sustain conditions conducive for life, while other planets, such as Mars, did not.

The research also gives scientists data that can be applied to the discovery of new exoplanets.

"There is special interest in defining this history--in reference to the huge number of exoplanet discoveries--to deduce whether events might have been similar or different in exo-solar systems," says John Tarduno, the William R. Kenan, Jr., Professor in the Department of Earth and Environmental Sciences and dean of research for Arts, Sciences & Engineering at Rochester. "This is another component of the search for other habitable planets."

SOLVING A PARADOX USING A METEORITE IN MEXICO

Some meteorites are pieces of debris from outer space objects such as asteroids. After breaking apart from their "parent bodies," these pieces are able to survive passing through the atmosphere and eventually hit the surface of a planet or moon.

Studying the magnetization of meteorites can give researchers a better idea of when the objects formed and where they were located early in the solar system's history.

"We realized several years ago that we could use the magnetism of meteorites derived from asteroids to determine how far these meteorites were from the sun when their magnetic minerals formed," Tarduno says.

In order to learn more about the origin of meteorites and their parent bodies, Tarduno and the researchers studied magnetic data collected from the Allende meteorite, which fell to Earth and landed in Mexico in 1969. The Allende meteorite is the largest carbonaceous chondrite meteorite found on Earth and contains minerals--calcium-aluminum inclusions--that are thought to be the first solids formed in the solar system. It is one of the most studied meteorites and was considered for decades to be the classic example of a meteorite from a primitive asteroid parent body.

In order to determine when the objects formed and where they were located, the researchers first had to address a paradox about meteorites that was confounding the scientific community: how did the meteorites gain magnetization?

Recently, a controversy arose when some researchers proposed that carbonaceous chondrite meteorites like Allende had been magnetized by a core dynamo, like that of Earth. Earth is known as a differentiated body because it has a crust, mantle, and core that are separated by composition and density. Early in their history, planetary bodies can gain enough heat so that there is widespread melting and the dense material--iron--sinks to the center.

New experiments by Rochester graduate student Tim O'Brien, the first author of the paper, found that magnetic signals interpreted by prior researchers was not actually from a core. Instead, O'Brien found, the magnetism is a property of Allende's unusual magnetic minerals.

DETERMINING JUPITER'S ROLE IN ASTEROID MIGRATION

Having solved this paradox, O'Brien was able to identify meteorites with other minerals that could faithfully record early solar system magnetizations.

Tarduno's magnetics group then combined this work with theoretical work from Eric Blackman, a professor of physics and astronomy, and computer simulations led by graduate student Atma Anand and Jonathan Carroll-Nellenback, a computational scientist at Rochester's Laboratory for Laser Energetics. These simulations showed that solar winds draped around early solar system bodies and it was this solar wind that magnetized the bodies.

Using these simulations and data, the researchers determined that the parent asteroids from which carbonaceous chondrite meteorites broke off arrived in the Asteroid Belt from the outer solar system about 4,562 million years ago, within the first five million years of solar system history.

Tarduno says the analyses and modeling offers more support for the so-called grand tack theory of the motion of Jupiter. While scientists once thought planets and other planetary bodies formed from dust and gas in an orderly distance from the sun, today scientists realize that the gravitational forces associated with giant planets--such as Jupiter and Saturn--can drive the formation and migration of planetary bodies and asteroids. The grand tack theory suggests that asteroids were separated by the gravitational forces of the giant planet Jupiter, whose subsequent migration then mixed the two asteroid groups.

He adds, "This early motion of carbonaceous chondrite asteroids sets the stage for further scattering of water-rich bodies--potentially to Earth--later in the development of the solar system, and it may be a pattern common to exoplanet systems."

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Leaving so soon? Unusual planetary nebula fades mere decades after it arrived

UNIVERSITY OF WASHINGTON

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IMAGE: TWO IMAGES OF THE STINGRAY NEBULA, LOCATED IN THE DIRECTION OF THE SOUTHERN CONSTELLATION ARA -- OR THE ALTAR -- CAPTURED 20 YEARS APART BY NASA'S HUBBLE SPACE TELESCOPE. THE... view more 

CREDIT: NASA/ESA/BRUCE BALICK/MARTÍN GUERRERO/GERARDO RAMOS-LARIOS

Stars are rather patient. They can live for billions of years, and they typically make slow transitions -- sometimes over many millions of years -- between the different stages of their lives.

So when a previously typical star's behavior rapidly changes in a few decades, astronomers take note and get to work.

Such is the case with a star known as SAO 244567, which lies at the center of Hen 3-1357, commonly known as the Stingray Nebula. The Stingray Nebula is a planetary nebula -- an expanse of material sloughed off from a star as it enters a new phase of old age and then heated by that same star into colorful displays that can last for up to a million years.

The tiny Stingray Nebula unexpectedly appeared in the 1980s and was first imaged by scientists in the 1990s using NASA's Hubble Space Telescope. It is by far the youngest planetary nebula in our sky. A team of astronomers recently analyzed a more recent image of the nebula, taken in 2016 by Hubble, and found something unexpected: As they report in a paper accepted to the Astrophysical Journal, the Stingray Nebula has faded significantly and changed shape over the course of just 20 years.

If dimming continues at current rates, in 20 or 30 years the Stingray Nebula will be barely perceptible, and was likely already fading when Hubble obtained the first clear images of it in 1996, according to lead author Bruce Balick, an emeritus professor of astronomy at UW.

"This is an unprecedented departure from typical behavior for a planetary nebula," said Balick. "Over time, we would expect it to imperceptibly brighten and expand, which could easily go unnoticed in a century or more. But here we're seeing the Stingray nebula fade significantly in an incredibly compressed time frame of just 20 years. Moreover, its brightest inner structure has contracted -- not expanded -- as the nebula fades."

Planetary nebulae form after most stars, including stars like our own sun, swell into red giants as they exhaust hydrogen fuel. At the end of the red giant phase, the star then expels large amounts of its outer material as it gradually -- over the course of a million years -- transforms into a small, compact white dwarf. The sloughed-off material expands outward for several thousand years while the star heats the material, which eventually becomes ionized and glows.

Balick and his co-authors, Martín Guerrero at the Institute of Astrophysics of Andalusia in Spain and Gerardo Ramos-Larios at the University of Guadalajara in Mexico, compared Hubble images of the Stingray Nebula taken in 1996 and 2016. Hen 3-1357 changed shape markedly over 20 years, losing the sharp, sloping edges that gave the Stingray Nebula its name. Its colors have faded overall and once-prominent blue expanses of gas near its center are largely gone.

"In a planetary nebula, the star is really the center of all the activity," said Balick. "The material around it is directly responsive to the energy from its parent star."

The team analyzed light spectra from Hen 3-1357 emitted by chemical elements in the nebula. Emission levels of hydrogen, nitrogen, sulfur and oxygen all dropped between 1996 and 2016, particularly oxygen, which dropped by a factor of 900. The resulting fade in color and the nebula's change in shape are likely connected to the cooling of its parent star -- from a peak of about 107,500 degrees Fahrenheit in 2002 to just under 90,000 degrees Fahrenheit in 2015 -- which means it is giving off less ultraviolet ionizing radiation that heats the expelled gas and makes it glow.

"Like a doused forest fire, the smoke wanes more slowly than the flames that created it," said Balick. "Even so, we were amazed when the Hubble images revealed how quickly the nebula was fading. It took a month of work to believe it."

Astronomers have yet to understand why SAO 244567 made the Stingray Nebula light up and then fade almost as quickly. One theory, posited by a team led by Nicole Reindl at the University of Potsdam, is that the star underwent a brief burst of fresh helium fusion around its core, which stirred up its outer layers and caused its surface to both shrink and heat.

If so, then as its outer layers settle back down, the star may return to a more typical transition from red giant to white dwarf. Only future observations of the star and its nebula can confirm this.

"Unfortunately, the best tool to follow future changes in the Stingray Nebula, the Hubble Space Telescope, is near the end of its life as well," said Balick. "We can hope, but the odds aren't good for Hubble's survival as its three remaining gyroscopes start to fail. It's a good race to the finish."

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The Hubble Space Telescope is an international partnership between NASA and the European Space Agency, or ESA, and managed by NASA's Goddard Space Flight Center in Maryland. The Space Telescope Science Institute is responsible for Hubble science operations. The research was also funded by the European Union and the National Council of Science and Technology in Mexico.

Hubble captures unprecedented fading of 

Stingray nebula

NASA/GODDARD SPACE FLIGHT CENTER

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IMAGE: THIS IMAGE COMPARES TWO DRASTICALLY DIFFERENT PORTRAITS OF THE STINGRAY NEBULA CAPTURED BY NASA'S HUBBLE SPACE TELESCOPE 20 YEARS APART. THE IMAGE ON THE LEFT, TAKEN WITH THE WIDE FIELD... view more 

CREDIT: CREDITS: NASA, ESA, B. BALICK (UNIVERSITY OF WASHINGTON), M. GUERRERO (INSTITUTO DE ASTROFÍSICA DE ANDALUCÍA), AND G. RAMOS-LARIOS (UNIVERSIDAD DE GUADALAJARA)

Astronomers have caught a rare look at a rapidly fading shroud of gas around an aging star. Archival data from NASA's Hubble Space Telescope reveal that the nebula Hen 3-1357, nicknamed the Stingray nebula, has faded precipitously over just the past two decades. Witnessing such a swift rate of change in a planetary nebula is exceeding rare, say researchers.

Images captured by Hubble in 2016, when compared to Hubble images taken in 1996, show a nebula that has drastically dimmed in brightness and changed shape. Bright, blue, fluorescent tendrils and filaments of gas toward the center of the nebula have all but disappeared, and the wavy edges that earned this nebula its aquatic-themed name are virtually gone. The young nebula no longer pops against the black velvet background of the vast universe.

"This is very, very dramatic, and very weird," said team member Martín A. Guerrero of the Instituto de Astrofísica de Andalucía in Granada, Spain. "What we're witnessing is a nebula's evolution in real time. In a span of years, we see variations in the nebula. We have not seen that before with the clarity we get with this view."

Researchers discovered unprecedented changes in the light emitted by glowing nitrogen, hydrogen, and oxygen being blasted off by the dying star at the center of the nebula. The oxygen emission, in particular, dropped in brightness by a factor of nearly 1,000 between 1996 and 2016.

"Changes in nebulae have been seen before, but what we have here are changes in the fundamental structure of the nebula," said Bruce Balick of the University of Washington, Seattle, leader of the new research. "In most studies, the nebula usually gets bigger. Here, it's fundamentally changing its shape and getting fainter, and doing so on an unprecedented time scale. Moreover, to our surprise, it's not growing any larger. Indeed, the once-bright inner elliptical ring seems to be shrinking as it fades."

Ground-based observations of other planetary nebulae have shown hints of changes in brightness over time, but those speculations haven't been confirmed until now. Only Hubble can resolve the changes in structure in this tiny nebula. The new paper examines every image of the Stingray nebula from Hubble's archives.

"Because of Hubble's optical stability, we are very, very confident that this nebula is changing in brightness with time," added Guerrero. "This is something that can only be confirmed with Hubble's visual acuity."

The researchers note the nebula's rapid changes are a response to its central star, SAO 244567, expanding due to a temperature drop, and in turn emitting less ionizing radiation.

A 2016 study by Nicole Reindl, now of the University of Potsdam, Germany, and a team of international researchers, also using Hubble data, noted the star at the center of the Stingray nebula, SAO 244567, is special in its own right.

Observations from 1971 to 2002 showed the temperature of the star skyrocketing from less than 40,000 to 108,000 degrees Fahrenheit, more than ten times hotter than the surface of our Sun. Now, Reindl and her research team has shown that SAO 245567 is cooling. Reindl speculates the temperature jump was caused by a brief flash of helium fusion that occurred in a shell around the core of the central star. Recently, the star appears to be backstepping into its early stage of stellar evolution.

"We're very lucky to observe it just in that moment," said Reindl. "During such a helium shell flash, it evolves very quickly, and that implies short evolutionary timescales, so we can't usually see how these stars evolve. We just happened to be there at the right time to have caught that."

The team studying the rapid fading of the Stingray nebula can only speculate at this time what's in store for the future of this young nebula. At its present rates of fading, it's estimated the nebula will barely be detectable in 20 or 30 years.

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The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

 

Gaia: astronomers to release most accurate data ever for nearly two billion stars

ROYAL ASTRONOMICAL SOCIETY

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IMAGE: A DIAGRAM OF THE TWO MOST IMPORTANT COMPANION GALAXIES TO THE MILKY WAY, THE LARGE MAGELLANIC CLOUD OR LMC (LEFT) AND THE SMALL MAGELLANIC CLOUD (SMC) MADE USING DATA FROM... view more 

CREDIT: ESA/GAIA/DPAC

On 3 December an international team of astronomers will announce the most detailed ever catalogue of the stars in a huge swathe of our Milky Way galaxy. The measurements of stellar positions, movement, brightness and colours are in the third early data release from the European Space Agency's Gaia space observatory and will be publicly available. Initial findings include the first optical measurement of the acceleration of the Solar system. The data set, and early scientific discoveries, will be presented at a special briefing hosted by the Royal Astronomical Society.

Launched in 2013, Gaia operates in an orbit around the so-called Lagrange 2 (L2) point, located 1.5 million kilometres behind the Earth in the direction away from the Sun. At L2 the gravitational forces between the Earth and Sun are balanced, so the spacecraft stays in a stable position, allowing long-term essentially unobstructed views of the sky.

The primary objective of Gaia is measure stellar distances using the parallax method. In this case astronomers use the observatory to continuously scan the sky, measuring the apparent change in the positions of stars over time, resulting from the Earth's movement around the Sun.

Knowing that tiny shift in the positions of stars allows their distances to be calculated. On Earth this is made more difficult by the blurring of the Earth's atmosphere, but in space the measurements are only limited by the optics of the telescope.

Two previous releases included the positions of 1.6 billion stars. This release brings the total to just under 2 billion stars, whose positions are significantly more accurate than in the earlier data. Gaia also tracks the changing brightness and positions of the stars over time across the line of sight (their so-called proper motion), and by splitting their light into spectra, measures how fast they are moving towards or away from the Sun and assesses their chemical composition.

The new data include exceptionally accurate measurements of the 300,000 stars within the closest 326 light years to the Sun. The researchers use these data to predict how the star background will change in the next 1.6 million years. They also confirm that the Solar system is accelerating in its orbit around the Galaxy.

This acceleration is gentle, and is what would be expected from a system in a circular orbit. Over a year the Sun accelerates towards the centre of the Galaxy by 7 mm per second, compared with its speed along its orbit of about 230 kilometres a second.

Gaia data additionally deconstruct the two largest companion galaxies to the Milky Way, the Small and Large Magellanic Clouds, allowing researchers to see their different stellar populations. A dramatic visualisation shows these subsets, and the bridge of stars between the two systems.

Dr Floor van Leeuwen of the Institute of Astronomy at the University of Cambridge, and UK Gaia DPAC Project Manager, comments: "Gaia is measuring the distances of hundreds of millions of objects that are many thousands of light years away, at an accuracy equivalent to measuring the thickness of hair at a distance of more than 2000 kilometres. These data are one of the backbones of astrophysics, allowing us to forensically analyse our stellar neighbourhood, and tackle crucial questions about the origin and future of our Galaxy."

Gaia will continue gathering data until at least 2022, with a possible mission extension until 2025. The final data releases are expected to yield stellar positions 1.9 times as accurate as those released so far, and proper motions more than 7 times more accurate, in a catalogue of more than 2 billion objects.

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Images and movies

A diagram of the two most important companion galaxies to the Milky Way, the Large Magellanic Cloud or LMC (left) and the Small Magellanic Cloud (SMC) made using data from the European Space Agency Gaia satellite. The two galaxies are connected by a 75,000 light-years long bridge of stars, some of which is seen extending from the left of the SMC.

Credit: ESA/Gaia/DPAC

Movies [available after the embargo expires]

Our Solar Neighbourhood

Since 2013 the European Space Agency Gaia satellite has been measuring the positions and characteristics of nearly two billion stars in our Milky Way galaxy. This movie is a flythrough of the nearest 326 light years to the Sun, a region of space that contains around 300,000 stars.

Credit: ESA/Gaia/DPAC

The Large and Small Magellanic Clouds

Data from the European Space Agency Gaia space observatory help us understand the different stellar populations in the two main companion galaxies to the Milky Way, the Large and Small Magellanic Clouds. This animation moves from an image of the Milky Way to the two systems, shows the separate populations of stars in each one. It then illustrates the dramatic bridge of stars connecting the LMC and SMC, spanning 75,000 light years.

Data sets provided by Merce Romero-Gomez. Video based on the paper: Gaia Early Data Release 3: structure and properties of the Magellanic Clouds by Gaia Collaboration, X. Luri et al., A&A 2020 (in press).

Credit: ESA/Gaia/DPAC

Further information

The Gaia Early Data Release 3 will be freely available to the scientific community and the wider public after 1100 GMT on Thursday 3 December.

Institutes in the UK have played a pivotal role in a wide range of aspects of the new Gaia data release. At the Royal Observatory Edinburgh, supported by Leicester University, software for the pre-processing of the data was prepared and tested; at the Institute of Astronomy (IoA) in Cambridge the photometric data was processed and prepared for publication, and at the Mullard Space Science Laboratory work is continuing on the software for the processing of the spectroscopic data produced by the mission. The UK activities in the Gaia project are supported by grants from the UK Space Agency and the Science and Technology Facilities Council.

Gaia space telescope measured the acceleration of the Solar System

UNIVERSITY OF HELSINKI

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IMAGE: THE STREAM OF STARS ACROSS THE SKY. view more 

CREDIT: (ESA AND GAIA DPAC)

The Gaia space telescope has measured the acceleration of the Solar System when it orbits the center of our Milky Way galaxy. The Solar System motion relative to the stars agrees with the results by Finnish astronomers in the 19th century.

Moreover, the observational data by Gaia improves satellite navigation. Finnish researchers are participating in this massive endeavor, that results in three-dimensional mapping of our galaxy, to be completed in 2024.

Today, Dec. 3, 2020, the European Space Agency (ESA) released observational data from the Gaia telescope (Gaia Early Data Release 3 or EDR3), in continuation to the DR1 and DR2 releases of the years 2016 and 2018. Gaia accrues accurate knowledge about, for example, the Milky Way stars, distant extragalactic quasars, and the asteroids of our Solar System.

Quasars are bright, star-like objects that allow for the determination of planet Earth's orientation in space. With the help of their precise positions measured by Gaia, a new high-precision reference system can be constructed for defining the positions of stars, Solar System objects, and also satellites.

"The knowledge accrued by Gaia affects the precision of satellite navigation in the future. The satellite positions and Earth orientation in space are determined in a reference frame tied to the directions of quasars. The precision and state of the art of the reference frame are critical for the precision in navigation," says Professor Markku Poutanen at the Finnish Geospatial Research Institute FGI, National Land Survey of Finland.

The precise observations of quasars resulted, for the first time, in a successful computation of the acceleration of the Solar System.

"The acceleration of the Solar System towards the center of the Milky Way, as measured by Gaia, is (2.32±0.16) x 10-10 m/s2 or, roughly, two one-hundred-billionth parts of the gravitational acceleration caused by the Earth on its surface, " summarizes Astronomy Professor Karri Muinonen at the Department of Physics, University of Helsinki, also Research Professor at the Finnish Geospatial Research Institute FGI.

Gaia in the research of asteroids

Gaia's data processing is carried out within the European DPAC network (Data Processing and Analysis Consortium) with more than 300 researchers. Solar System researchers at the University of Helsinki take part in the Gaia data processing in several different ways.

"We are responsible for the daily computation of orbits for asteroids discovered by Gaia. Based on these computations, ground-based follow-up observations are organized," describes Muinonen.

"Before data releases, we take part in the validation of Gaia observations of asteroid positions, brightnesses, and spectra. Our research with Gaia data focuses on asteroid orbits, rotation periods and pole orientations, masses, shapes, and surface structural and compositional properties. In the computation of collision probabilities for near-Earth asteroids, the precision of reference frames is completely central," continues Muinonen.

Asteroid observations by Gaia were published in DR2 in spring 2018 (14 099 asteroids). In the forthcoming DR3 release in spring 2022, there will be position and brightness data for tens of thousands of asteroids and, for the first time, asteroid spectra will also be released.

Years of work and billions of stars

The EDR3 data has been collected by Gaia from the end of July 2014. The data includes, for example, position and brightness data of 1,81 billion stars and color data of 1,55 billion stars from the time period of 34 months. Furthermore, the data more than triples the number of quasars observed for precise reference frames to 1,61 million.

EDR3 is a remarkable improvement, in terms of both numbers and precisions, as compared to the earlier releases. The newest release gives hints about the gigantic nature of the forthcoming DR3 release in spring 2022 and the final DR4 release after 2024.

Gaia observes astronomical objects systematically in the so-called L2 Lagrange point some 1,5 million kilometers from the Earth in the anti-sun direction. Gaia observes about two billion stars with a precision, at best, of one hundred millionths of a degree. The result will be a three-dimensional map of our galaxy.

Stellar motion in the future

Based on the Gaia data, researchers' have modeled the motion of stars in the Milky Way. They have produced an animation for the motion of 40 000 randomly selected stars on the sky 1.6 million years into the future.

"In the animation, short and long trails describe changes in stellar positions with 80 000 years. The former are mostly related to distant stars, whereas the latter are solely due to the nearby stars. Every now and then, short trails expand into long ones, and long trails shrink into short ones. This is also related to the changing distances of the stars," says Muinonen.

In the end of the animation, stars appear to be removed from the left and collected to the right. This is due to the Solar System's motion relative to the stars. A similar phenomenon can be seen when moving from a center of a forest islet to its boundary: the trees in the front gradually disappear whereas they seem to be collected in the back.

"This shows the average motion of the Solar System with respect to the surrounding stars. From the Finnish point of view, it is intriguing that the motion documented by Gaia agrees with the pioneering research about the Solar System's motion by Friedrich Wilhelm August Argelander (1799-1875) in the 19th century at the Helsinki Observatory," concludes Muinonen.

Argelander was the first astronomer, who unequivocally calculated the direction of Solar System motion in space. He worked at the Observatory, University of Helsinki, then the Imperial Alexander University. He had made the observations at the Turku Observatory in 1827-1831 before the observatory moved to Helsinki. In Helsinki, he compiled the stellar catalog entitled "DLX stellarum fixarum positiones mediae ineunte anno 1830" that, as the title says, included the precise positions of 560 stars.

Movement of quasars is actually the movement of Solar System

More accurately, the apparent stellar streams include the information about the motion of the stars and the Solar System about the center of the Milky Way. The Gaia quasar observations allow for the determination of the acceleration related to this orbital motion.

Gaia has measured the apparent motions of quasars on the sky. These motions are tiny, about one thousandth part of the motion of stars 3000 light years from us. The apparent stream of quasars is directed toward the center of the Milky Way, that is, in the direction where the acceleration of the Solar System is pointing. Gaia has, in essence, measured the absolute motion of the Solar System relative to the distant universe. This motion derives from the gravitational forces by the Milky Way and all other objects in the universe.

CAPTION

Figure: The acceleration of the Solar System is revealed in the apparent motion of the distant quasars toward the center of the Milky Way. In reality, the quasars do not have proper motion.

CREDIT

(ESA and Gaia DPAC)

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Animation: The stars' predicted motion across the sky. (ESA and Gaia DPAC) https://youtu.be/cEsfqFDSpm0

Read more:

Gaia EDR3 (3. 12. 2020) data release, home page:

https://www.cosmos.esa.int/web/gaia/early-data-release-3

http://www.esa.int/Science_Exploration/Space_Science/Gaia

More information:

Professor Karri Muinonen, University of Helsinki and National Land Survey, karri.muinonen@helsinki.fi, +358 50 415 5474, Asteroid shapes, rotations, and surface properties from Gaia photometry

Professor Markku Poutanen, National Land Survey, markku.poutanen@maanmittauslaitos.fi, +358 40 718 2152, Reference frames

Docent Mikael Granvik, University of Helsinki and Luleå Institute of Technology, mikael.granvik@helsinki.fi, +358 50 521 7209, Asteroid orbit and mass computation from Gaia astrometry

Docent Antti Penttilä, University of Helsinki, antti.i.penttila@helsinki.fi, +358 50 524 0968, Asteroid compositional analyses from Gaia spectroscopy