From The National Aeronautics Space Agency (US)
Feb 1, 2022
Elizabeth Landau
NASA Headquarters
elandau@nasa.gov
The Milky Way. Credit: R. Hurt/The National Aeronautics and Space Agency(US) JPL-Caltech(US) The bar is visible in this image.
Pictures of the Milky Way show billions of stars arranged in a spiral pattern radiating out from the center, with illuminated gas in between. But our eyes can only glimpse the surface of what holds our galaxy together. About 95 percent of the mass of our galaxy is invisible and does not interact with light. It is made of a mysterious substance called Dark Matter, which has never been directly measured.
Now, a new study calculates how Dark Matter’s gravity affects objects in our solar system, including spacecraft and distant comets. It also proposes a way that Dark Datter’s influence could be directly observed with a future experiment. The article is published in the MNRAS.
“We’re predicting that if you get out far enough in the solar system, you actually have the opportunity to start measuring the Dark Matter force,” said Jim Green, study co-author and advisor to NASA’s Office of the Chief Scientist. “This is the first idea of how to do it and where we would do it.”
Dark matter in our backyard
Here on Earth, our planet’s gravity keeps us from flying out of our chairs, and the Sun’s gravity keeps our planet orbiting on a 365-day schedule. But the farther from the Sun a spacecraft flies, the less it feels the Sun’s gravity, and the more it feels a different source of gravity: that of the matter from the rest of the galaxy, which is mostly Dark Matter. The mass of our galaxy’s 100 billion stars is miniscule compared to estimates of the Milky Way’s Dark Matter content.
To understand the influence of Dark Matter in the solar system, lead study author Edward Belbruno calculated the “galactic force,” the overall gravitational force of normal matter combined with Dark Matter from the entire galaxy. He found that in the solar system, about 45 percent of this force is from Dark Matter and 55 percent is from normal, so-called “baryonic matter.” This suggests a roughly half-and-half split between the mass of Dark Matter and normal matter in the solar system.
“I was a bit surprised by the relatively small contribution of the galactic force due to Dark Matter felt in our solar system as compared to the force due to the normal matter,” said Belbruno, mathematician and astrophysicist at Princeton University (US) and Yeshiva University (US). “This is explained by the fact most of Dark Matter is in the outer parts of our galaxy, far from our solar system.”
A large region called a “halo” of Dark Matter encircles the Milky Way and represents the greatest concentration of the Dark Matter of the galaxy.
There is little to no normal matter in the halo. If the solar system were located at a greater distance from the center of the galaxy, it would feel the effects of a larger proportion of Dark Matter in the galactic force because it would be closer to the dark matter halo, the authors said.
In this artist’s conception, NASA’s Voyager 1 spacecraft has a bird’s-eye view of the solar system.
National Aeronautics Space Agency(US) Voyager 1.
The circles represent the orbits of the major outer planets: Jupiter, Saturn, Uranus, and Neptune. Launched in 1977, Voyager 1 visited the planets Jupiter and Saturn. The spacecraft is now more than 14 billion miles from Earth, making it the farthest human-made object ever built.
In fact, Voyager 1 is now zooming through interstellar space, the region between the stars that is filled with gas, dust, and material recycled from dying stars.
National Aeronautics Space Agency (US) Heliosphere-heliopause showing positions of two Voyager spacecraft. Credit: NASA/JPL-Caltech.
Credits: G. Bacon (The Space Telescope Science Institute (US)). NASA, The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU).
How Dark Matter may influence spacecraft
Green and Belbruno predict that Dark Matter’s gravity ever so slightly interacts with all of the spacecraft that NASA has sent on paths that lead out of the solar system, according to the new study.
“If spacecraft move through the Dark Matter long enough, their trajectories are changed, and this is important to take into consideration for mission planning for certain future missions,” Belbruno said.
Such spacecraft may include the retired Pioneer 10 and 11 probes that launched in 1972 and 1973, respectively; the Voyager 1 and 2 probes that have been exploring for more than 40 years and have entered interstellar space; and the New Horizons spacecraft that has flown by Pluto and Arrokoth in the Kuiper Belt.
NASA Pioneer 10
NASA Pioneer 11.
National Aeronautics Space Agency(USA) New Horizons(US) spacecraft.
Kuiper Belt. Minor Planet Center.
But it’s a tiny effect. After traveling billions of miles, the path of a spacecraft like Pioneer 10 would only deviate by about 5 feet (1.6 meters) due to the influence of Dark Matter. “They do feel the effect of Dark Matter, but it’s so small, we can’t measure it,” Green said.
Where does the galactic force take over?
At a certain distance from the Sun, the galactic force becomes more powerful than the pull of the Sun, which is made of normal matter. Belbruno and Green calculated that this transition happens at around 30,000 astronomical units, or 30,000 times the distance from Earth to the Sun. That is well beyond the distance of Pluto, but still inside the Oort Cloud, a swarm of millions of comets that surrounds the solar system and extends out to 100,000 astronomical units.
Milky Way Galaxy from Sun to Interstellar Space beyond the Oort Cloud. Credit: NASA/ JPL-Caltech.
This means that Dark Matter’s gravity could have played a role in the trajectory of objects like ‘Oumuamua, the cigar-shaped comet or asteroid that came from another star system and passed through the inner solar system in 2017. Its unusually fast speed could be explained by Dark Matter’s gravity pushing on it for millions of years, the authors say.
If there is a giant planet in the outer reaches of the solar system, a hypothetical object called Planet 9 or Planet X that scientists have been searching for in recent years, Dark Matter would also influence its orbit. If this planet exists, Dark Matter could perhaps even push it away from the area where scientists are currently looking for it, Green and Belbruno write. Dark Matter may have also caused some of the Oort Cloud comets to escape the orbit of the Sun altogether.
Could Dark Matter’s gravity be measured?
To measure the effects of Dark Matter in the solar system, a spacecraft wouldn’t necessarily have to travel that far. At a distance of 100 astronomical units, a spacecraft with the right experiment could help astronomers measure the influence of Dark Matter directly, Green and Belbruno said.
Specifically, a spacecraft equipped with radioisotope power, a technology that has allowed Pioneer 10 and 11, the Voyagers, and New Horizon to fly very far from the Sun, may be able to make this measurement. Such a spacecraft could carry a reflective ball and drop it at an appropriate distance. The ball would feel only galactic forces, while the spacecraft would experience a thermal force from the decaying radioactive element in its power system, in addition to the galactic forces. Subtracting out the thermal force, researchers could then look at how the galactic force relates to deviations in the respective trajectories of the ball and the spacecraft. Those deviations would be measured with a laser as the two objects fly parallel to one another.
A proposed mission concept called Interstellar Probe, which aims to travel to about 500 astronomical units from the Sun to explore that uncharted environment, is one possibility for such an experiment.
Two views from Hubble of the massive galaxy cluster Cl 0024+17 (ZwCl 0024+1652) are shown. To the left is the view in visible-light with odd-looking blue arcs appearing among the yellowish galaxies. These are the magnified and distorted images of galaxies located far behind the cluster. Their light is bent and amplified by the immense gravity of the cluster in a process called “gravitational lensing”.
National Aeronautics and Space Administration(US)/The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Hubble Space Telescope.
Gravitational Lensing National Aeronautics Space Agency (US) and European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU).
To the right, a blue shading has been added to indicate the location of invisible material called Dark Matter that is mathematically required to account for the nature and placement of the gravitationally lensed galaxies that are seen.
Credits: M.J. Jee and H. Ford (Johns Hopkins University(US)) NASA, ESA.
More about Dark Matter
Dark Matter as a hidden mass in galaxies was first proposed in the 1930s by Fritz Zwicky. But the idea remained controversial until the 1960s and 1970s, when Vera C. Rubin and colleagues confirmed that the motions of stars around their galactic centers would not follow the laws of physics if only normal matter were involved. Only a gigantic hidden source of mass can explain why stars at the outskirts of spiral galaxies like ours move as quickly as they do. [See Dark Matter Background below.]
Today, the nature of Dark Matter is one of the biggest mysteries in all of astrophysics. Powerful observatories like the Hubble Space Telescope and the Chandra X-Ray Observatory have helped scientists begin to understand the influence and distribution of Dark Matter in the universe at large.
The National Aeronautics and Space Administration Chandra X-ray telescope(US).
Hubble has explored many galaxies whose Dark Matter contributes to an effect called “lensing,” where gravity bends space itself and magnifies images of more distant galaxies.
Astronomers will learn more about Dark Matter in the cosmos with the newest set of state-of-the-art telescopes. NASA’s James Webb Space Telescope, which launched Dec. 25, 2021, will contribute to our understanding of Dark Matter by taking images and other data of galaxies and observing their lensing effects.
National Aeronautics Space Agency(US)/European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope(US) annotated, finally launched December 25, 2021, ten years late.
NASA’s Nancy Grace Roman Space Telescope, set to launch in the mid-2020s, will conduct surveys of more than a billion galaxies to look at the influence of dark matter on their shapes and distributions.
The European Space Agency’s forthcoming Euclid mission, which has a NASA contribution, will also target Dark Matter (and dark energy, looking back in time about 10 billion years to a period when dark energy began hastening the universe’s expansion).
And the Vera C. Rubin Observatory, a collaboration of The National Science Foundation (US), The Department of Energy (US), and others, which is under construction in Chile, will add valuable data to this puzzle of dark matter’s true essence.
The National Science Foundation (US) NOIRLab (US) National Optical Astronomy Observatory (US) Vera C. Rubin Observatory [LSST] Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing NSF (US) NOIRLab (US) NOAO (US) The Association of Universities for Research in Astronomy (AURA)(US) Gemini South Telescope and Southern Astrophysical Research Telescope.
But these powerful tools are designed to look for Dark Matter’s strong effects across large distances, and much farther afield than in our solar system, where Dark Matter’s influence is so much weaker.
“If you could send a spacecraft out there to detect it, that would be a huge discovery,” Belbruno said.
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Dark Matter Background
Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM, denied the Nobel, some 30 years later, did most of the work on Dark Matter.
Fritz Zwicky.
Coma cluster via NASA/ESA Hubble, the original example of Dark Matter discovered during observations by Fritz Zwicky and confirmed 30 years later by Vera Rubin.
In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.
Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).
Vera Rubin measuring spectra, worked on Dark Matter(Emilio Segre Visual Archives AIP SPL).
Dark Matter Research
Super Cryogenic Dark Matter Search from DOE’s SLAC National Accelerator Laboratory (US) at Stanford University (US) at SNOLAB (Vale Inco Mine, Sudbury, Canada).
DAMA at Gran Sasso uses sodium iodide housed in copper to hunt for dark matter LNGS-INFN.
Yale HAYSTAC axion dark matter experiment at Yale’s Wright Lab.
The LBNL LZ Dark Matter Experiment (US) Dark Matter project at SURF, Lead, SD, USA.
PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China.
Inside the Axion Dark Matter eXperiment U Washington (US) Credit : Mark Stone U. of Washington. Axion Dark Matter Experiment.
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See the full article here .
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The The National Aeronautics and Space Administration (US) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.
President Dwight D. Eisenhower established the National Aeronautics and Space Administration in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.
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NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA] Greenhouse Gases Observing Satellite.
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