NASA scientists study how to remove planetary “photobombers”
IMAGE: ARTIST’S CONCEPT OF KEPLER-186F, AN EARTH-SIZE EXOPLANET ORBITING A RED DWARF STAR IN THE CONSTELLATION CYGNUS. view more
CREDIT: NASA/TIM PYLE
Imagine you go to a theme park with your family and you ask a park employee to take a group photo. A celebrity walks by in the background and waves at the camera, stealing the focus of the photo. Surprisingly, this concept of “photobombing” is relevant to astronomers looking for habitable planets, too.
When scientists point a telescope at an exoplanet, the light the telescope receives could effectively be “contaminated” by light from other planets in the same star system, according to a new NASA study. The research, published in the Astrophysical Journal Letters on Aug. 11, modeled how this “photobombing” effect would impact an advanced space telescope designed to observe potentially habitable exoplanets and suggested potential ways to overcome this challenge.
“If you looked at Earth sitting next to Mars or Venus from a distant vantage point, then depending on when you observed them, you might think they’re both the same object,” explains Dr. Prabal Saxena, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who led the research.
Saxena uses our own solar system as an analog to explain this photobombing effect.
“For example, depending on the observation, an exo-Earth could be hiding in [light from] what we mistakenly believe is a large exo-Venus,” said Dr. Saxena. Earth’s neighbor Venus is generally thought to be hostile to habitability, with surface temperatures hot enough to melt lead – so this mixing could lead scientists to miss out on a potentially habitable planet.
Astronomers use telescopes to analyze light from distant worlds to gather information that may reveal whether they could support life. One light-year, the distance light travels in a year, is almost six trillion miles (over nine trillion kilometers), and there are about 30 stars similar to our Sun within roughly 30 light-years of our solar system.
This photobombing phenomenon, in which observations of one planet are contaminated by light from other planets in a system, stems from the “point-spread function” (PSF) of the target planet. The PSF is an image created due to diffraction of light (the bending or spreading of light waves around an opening) coming from a source and is larger than the source for something very far away (such as an exoplanet). The size of the PSF of an object depends on the size of the telescope aperture (the light-collecting area) and wavelength at which the observation is taken. For worlds around a distant star, a PSF may resolve in such a way that two nearby planets or a planet and a moon could seem to morph into one.
If that is the case, the data that scientists can gather about such an Earth analog would be skewed or affected by whatever world or worlds were photobombing the planet in question, which could complicate or outright prevent the detection and confirmation of an exo-Earth, a potential planet like Earth beyond our solar system.
This is a cartoon illustrating the planetary photobombing concept. Photobombers like Mars and the Moon could sneak into a picture of Earth, if you tried to observe it in a way similar to how scientists will try to find and understand potentially habitable worlds outside our solar system.
CREDIT
NASA/Jay Friedlander/Prabal Saxena
Saxena examined an analogous scenario in which otherworldly astronomers might be looking at Earth from more than 30 light-years away, using a telescope similar to that recommended in the 2020 Astrophysics Decadal Survey. “We found that such a telescope would sometimes see potential exo-Earths beyond 30 light-years distance blended with additional planets in their systems, including those that are outside of the habitable zone, for a range of different wavelengths of interest,” Saxena said.
The habitable zone is that region of space around a star where the amount of starlight would allow liquid water on a planet’s surface, which may enable the existence of life.
There are multiple strategies to deal with the photobombing problem. These include developing new methods of processing data gathered by telescopes to mitigate the potential that photobombing will skew the results of a study. Another method would be to study systems over time, to avoid the possibility that planets with close orbits would appear in each other’s PSFs. Saxena’s study also discusses how using observations from multiple telescopes or increasing the size of the telescope could reduce the photobombing effect at similar distances.
Discovering exoplanets and determining if any can support life is part of NASA’s mission to explore and understand the unknown, to inspire and benefit humanity.
The research was funded by NASA under award number 80GSFC21M0002 and was also funded in part by the Goddard Sellers Exoplanet Environments Collaboration (SEEC).
JOURNAL
The Astrophysical Journal Letters
METHOD OF RESEARCH
Computational simulation/modeling
ARTICLE TITLE
Photobombing Earth 2.0: Diffraction-limit-related Contamination and Uncertainty in Habitable Planet Spectra
ARTICLE PUBLICATION DATE
11-Aug-2022
New discovery may offer clues to
"missing" pulsars
IMAGE: RADIO DETECTION OF AN ELUSIVE MILLISECOND PULSAR, PSR J1740-5340B (NGC 6397B), IN THE GLOBULAR CLUSTER NGC 6397 WITH THE PARKES RADIO TELESCOPE IN AUSTRALIA. view more
CREDIT: NAOC/SCIENCEAPE
Millisecond pulsars (MSPs) are evolved neutron stars with short spin periods that have gone through a long period of mass transfer in a low-mass X-ray binary phase. Globular clusters (GCs) - conglomerations of tens of thousands or millions of stars - are prolific environments for the formation of MSPs. However, in NGC 6397 - one of two GCs closest to Earth - only one MSP had been identified until recently.
Now researchers have not only found a second pulsar in our neighboring GC but have a better idea why other pulsars have "gone missing."
Using the Parkes radio telescope in Australia to observe NGC 6397, Dr. ZHANG Lei from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) discovered a new 5.78 ms-period MSP, named PSR J1740-5340B (NGC 6397B), in an eclipsing binary system. This discovery was confirmed by the MeerKAT radio telescope in South Africa.
NGC 6397B is detectable only when the pulsar is on the side of its orbit closest to the observer. Its measured orbital period of 1.97 days is the longest among all eclipsing binaries in GCs. This orbital period is also consistent with that of the previously discovered X-ray source U18, which was once considered a "hidden MSP." U18 has now been confirmed by the current research to be NGC 6397B.
The work was published in The Astrophysical Journal Letters on July 28.
Prof. LI Di of NAOC, the corresponding author, organized the first coherently de-dispersed search for new pulsars in NGC 6397 using the ultra-wideband low (UWL) receiver system recently installed on the Parkes radio telescope.
Using data from the first observation by the Parkes radio telescope on April 12, 2019, Dr. ZHANG discovered the new pulsar. In total, 39 observations were made by the Parkes radio telescope over a period of three years along with two observations by the MeerKAT radio telescope.
A notable characteristic of NGC 6397B is the faintness of its radio signal and extended radio-quiescent periods. The researchers suggested that NGC 6397B may be representative of a subgroup of extremely faint and heavily obscured binary pulsars. The researchers said this could explain the apparent overabundance of isolated pulsars in the dense cores of GCs, where stellar interactions are expected to preferentially result in binaries. In other words, binaries may not be absent - they may just be hard to detect.
According to the researchers, these faint pulsars are hard to pick up in radio bands either because they are embedded in clouds of plasma or are actively accreting matter due to their companion stars.
Future research may test whether these explanations correctly describe why few binary pulsars have been found in GCs.
JOURNAL
The Astrophysical Journal Letters
ARTICLE TITLE
Radio Detection of an Elusive Millisecond Pulsar in the Globular Cluster NGC 6397
Mars model provides method for landing humans on Red Planet
Peer-Reviewed PublicationA mathematical model developed by space medicine experts from The Australian National University (ANU) could be used to predict whether an astronaut can safely travel to Mars and fulfil their mission duties upon stepping foot on the Red Planet.
The ANU team simulated the impact of prolonged exposure to zero gravity on the cardiovascular system to determine whether the human body can tolerate Mars’ gravitational forces -- which aren’t as strong as on Earth -- without fainting or suffering a medical emergency when stepping out of a spacecraft.
The model could be used to assess the impact of short and long duration space flight on the body and could serve as another important piece of the puzzle in helping land humans on Mars.
Dr Lex van Loon, a Research Fellow from the ANU Medical School, said although there are multiple risks associated with travelling to Mars, the biggest concern is prolonged exposure to microgravity – near zero gravity – which, combined with exposure to damaging radiation from the Sun, could cause “fundamental” changes to the body.
“We know it takes about six to seven months to travel to Mars and this could cause the structure of your blood vessels or the strength of your heart to change due to the weightlessness experienced as a result of zero gravity space travel,” Dr van Loon, who is also the lead author of the paper, said.
“With the rise of commercial space flight agencies like Space X and Blue Origin, there’s more room for rich but not necessarily healthy people to go into space, so we want to use mathematical models to predict whether someone is fit to fly to Mars.”
Astrophysicist and emergency medicine registrar Dr Emma Tucker said prolonged exposure to zero gravity can cause the heart to become lazy because it doesn’t have to work as hard to overcome gravity in order to pump blood around the body.
“When you’re on Earth, gravity is pulling fluid to the bottom half of our body, which is why some people find their legs begin to swell up toward the end of the day. But when you go into space that gravitational pull disappears, which means the fluid shifts to the top half of your body and that triggers a response that fools the body into thinking there’s too much fluid,” Dr Tucker said.
“As a result, you start going to the toilet a lot, you start getting rid of extra fluid, you don’t feel thirsty and you don’t drink as much, which means you become dehydrated in space.
“This is why you might see astronauts on the news faint when they step foot on Earth again. This is quite a common occurrence as a result of space travel, and the longer you’re in space the more likely you are to collapse when you return to gravity.
“The purpose of our model is to predict, with great accuracy, whether an astronaut can safely arrive on Mars without fainting. We believe it’s possible.”
Due to a communication delay in relaying messages between Mars and Earth, astronauts must be able to out their duties without receiving immediate assistance from support crews. Dr van Loon said this window of radio silence differs depending on the alignment of the Sun, Earth and Mars in its orbit, but could last for at least 20 minutes.
“If an astronaut faints when they first step out of the spacecraft or if there’s a medical emergency, they’ll be nobody on Mars to help them,” Dr van Loon said.
“This is why we must be absolutely certain the astronaut is fit to fly and can adapt to Mars’ gravitational field. They must be able to operate effectively and efficiently with minimal support during those crucial first few minutes.”
The model uses an algorithm based on astronaut data collected from past space expeditions, including the Apollo Missions, to simulate the risks involved with travelling to Mars.
Although the space data used to inform the parameters of the model is derived from middle-aged and well-trained astronauts, the researchers hope to expand its capabilities by simulating the impact of prolonged space travel on relatively unhealthy individuals with pre-existing heart conditions. This would provide the researchers with a more holistic picture of what would happen if an “everyday” person was to travel into space.
The researchers’ work is published in the journal npj Microgravity.
JOURNAL
npj Microgravity
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Computational modeling of orthostatic intolerance for travel to Mars
ARTICLE PUBLICATION DATE
9-Aug-2022
Black hole collisions could help us measure how fast the universe is expanding
UChicago astronomers propose ‘spectral siren’ method
to understand evolution of the universe
Peer-Reviewed PublicationA black hole is usually where information goes to disappear—but scientists may have found a trick to use its last moments to tell us about the history of the universe. In a new study, two University of Chicago astrophysicists laid out a method for how to use pairs of colliding black holes to measure how fast our universe is expanding—and thus understand how the universe evolved, what it is made out of, and where it’s going. In particular, the scientists think the new technique, which they call a “spectral siren,” may be able to tell us about the otherwise elusive “teenage” years of the universe.
A cosmic ruler
A major ongoing scientific debate is exactly how fast the universe is expanding—a number called the Hubble constant. The different methods available so far yield slightly different answers, and scientists are eager to find alternate ways to measure this rate. Checking the accuracy of this number is especially important because it affects our understanding of fundamental questions like the age, history and makeup of the universe.
The new study offers a way to make this calculation, using special detectors that pick up the cosmic echoes of black hole collisions.
Occasionally, two black holes will slam into each other—an event so powerful that it literally creates a ripple in space-time that travels across the universe. Here on Earth, the U.S. Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Italian observatory Virgo can pick up those ripples, which are called gravitational waves.
Over the past few years, LIGO and Virgo have collected the readings from almost 100 pairs of black holes colliding.
The signal from each collision contains information about how massive the black holes were. But the signal has been traveling across space, and during that time the universe has expanded, which changes the properties of the signal. “For example, if you took a black hole and put it earlier in the universe, the signal would change and it would look like a bigger black hole than it really is,” explained UChicago astrophysicist Daniel Holz, one of the two authors on the paper.
If scientists can figure out a way to measure how that signal changed, they can calculate the expansion rate of the universe. The problem is calibration: How do they know how much it changed from the original?
In their new paper, Holz and first author Jose María Ezquiaga suggest that they can use our newfound knowledge about the whole population of black holes as a calibration tool. For example, current evidence suggests that most of the detected black holes have between five and 40 times the mass of our sun. “So we measure the masses of the nearby black holes and understand their features, and then we look further away and see how much those further ones appear to have shifted,” said Ezquiaga, a NASA Einstein Postdoctoral Fellow and Kavli Institute for Cosmological Physics Fellow working with Holz at UChicago. “And this gives you a measure of the expansion of the universe.”
The authors dub it the “spectral siren” method, a new approach to the ‘standard siren’ method which Holz and collaborators have been pioneering. (The name is a reference to the ‘standard candle’ methods also used in astronomy.)
The scientists are excited because in the future, as LIGO’s capabilities expand, the method may provide a unique window into the “teenage” years of the universe—about 10 billion years ago—that are hard to study with other methods.
Researchers can use the cosmic microwave background to look at the very earliest moments of the universe, and they can look around at galaxies near our own galaxy to study the universe’s more recent history. But the in-between period is harder to reach, and it’s an area of special scientific interest.
“It’s around that time that we switched from dark matter being the predominant force in the universe to dark energy taking over, and we are very interested in studying this critical transition,” said Ezquiaga.
The other advantage of this method, the authors said, is that there are fewer uncertainties created by gaps in our scientific knowledge. “By using the entire population of black holes, the method can calibrate itself, directly identifying and correcting for errors,” Holz said. The other methods used to calculate the Hubble constant rely on our current understanding of the physics of stars and galaxies, which involves a lot of complicated physics and astrophysics. This means the measurements might be thrown off quite a bit if there’s something we don’t yet know.
By contrast, this new black hole method relies almost purely on Einstein’s theory of gravity, which is well-studied and has stood up against all the ways scientists have tried to test it so far.
The more readings they have from all black holes, the more accurate this calibration will be. “We need preferably thousands of these signals, which we should have in a few years, and even more in the next decade or two,” said Holz. “At that point it would be an incredibly powerful method to learn about the universe.”
JOURNAL
Physical Review Letters
ARTICLE TITLE
Spectral sirens: Cosmology from the full mass distribution of compact binaries
