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By NASA
X-ray: NASA/CXC/CfA/Stroe, A. et al.; Optical: PanSTARRS; Radio: ASTRON/LOFAR; Image Processing: NASA/CXC/SAO/N. Wolk New observations from NASA’s Chandra X-ray Observatory and other telescopes have captured a rare cosmic event: two galaxy clusters have collided and are now poised to head back for another swipe at each other.
Galaxy clusters are some of the largest structures in the Universe. Held together by gravity, they are monster-sized collections of hundreds or thousands of individual galaxies, massive amounts of superheated gas, and invisible dark matter.
The galaxy cluster PSZ2 G181.06+48.47 (PSZ2 G181 for short) is about 2.8 billion light-years from Earth. Previously, radio observations from the LOw Frequency ARray (LOFAR), an antenna network in the Netherlands, spotted parentheses-shaped structures on the outside of the system. In this new composite image, X-rays from Chandra (purple) and ESA’s XMM-Newton (blue) have been combined with LOFAR data (red) and an optical image from Pan-STARRs of the stars in the field of view.
These structures are probably shock fronts — similar to those created by jets that have broken the sound barrier — likely caused by disruption of gas from the initial collision about a billion years ago. Since the collision they have continued traveling outwards and are currently separated by about 11 million light-years, the largest separation of these kinds of structures that astronomers have ever seen.
Colliding galaxy clusters PSZ2 G181.06+48.47 (Labeled).X-ray: NASA/CXC/CfA/Stroe, A. et al.; Optical: PanSTARRS; Radio: ASTRON/LOFAR; Image Processing: NASA/CXC/SAO/N. Wolk Now, data from NASA’s Chandra and ESA’s XMM-Newton is providing evidence that PSZ2 G181 is poised for another collision. Having a first pass at ramming each other, the two clusters have slowed down and begun heading back toward a second crash.
Astronomers made a detailed study of the X-ray observations of this collision site and found three shock fronts. These are aligned with the axis of the collision, and the researchers think they are early signs of the second, oncoming crash.
The researchers are still trying to determine how much mass each of the colliding clusters contains. Regardless, the total mass of the system is less than others where galaxy clusters have collided. This makes PSZ2 G181 an unusual case of a lower-mass system involved in the rare event of colliding galaxy clusters.
A paper describing these results appears in a recent issue of The Astrophysical Journal (ApJ) and is led by Andra Stroe from the Center for Astrophysics | Harvard & Smithsonian (CfA) and collaborators. It is part of a series of three papers in ApJ. The second paper is led by Kamlesh Rajpurohit, also of CfA, and the third paper is led by Eunmo Ahn, from Yonsei University in the Republic of Korea.
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
In this release, a composite image illustrates a dramatic cosmic story unfolding 2.8 billion light years from Earth. Presented both with and without labels, the image details the fallout when two galaxy clusters collide.
At the center of the image are the colliding galaxy clusters, which together are known as PSZ2 G181. This combined cluster somewhat resembles an irregular violet peanut shell, with bulbous ends linked by a tapered middle. Inside each bulbous end are several glowing dots; some of the galaxies within the clusters. The violet peanut shape is tilted at a slight angle, surrounded by a blue haze of X-ray gas.
Far from the bulbous ends, at our upper left and lower right, are two blotchy, thick red lines. These are probably shock fronts, similar to those created by jets that have broken the sound barrier. Bracketing the combined galaxy cluster, these shock fronts were caused by the initial collision about a billion years ago. They are currently separated by 11 million light-years.
New data from the Chandra and XMM-Newton observatories suggests that PSZ2 G181 is poised for another powerful cosmic event. Having already taken one swipe at each other, the two clusters within are once again on a collision course.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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Last Updated Jun 04, 2025 Related Terms
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This NASA Hubble Space Telescope image of NGC 520 offers one example of possible encounter scenarios between our Milky Way and the Andromeda galaxy. NGC 520 is the product of a collision between two disk galaxies that started 300 million years ago. Credits:
NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and B. Whitmore (STScI) As far back as 1912, astronomers realized that the Andromeda galaxy — then thought to be only a nebula — was headed our way. A century later, astronomers using NASA’s Hubble Space Telescope were able to measure the sideways motion of Andromeda and found it was so negligible that an eventual head-on collision with the Milky Way seemed almost certain.
A smashup between our own galaxy and Andromeda would trigger a firestorm of star birth, supernovae, and maybe toss our Sun into a different orbit. Simulations had suggested it was as inevitable as, in the words of Benjamin Franklin, “death and taxes.”
But now a new study using data from Hubble and the European Space Agency’s (ESA) Gaia space telescope says “not so fast.” Researchers combining observations from the two space observatories re-examined the long-held prediction of a Milky Way – Andromeda collision, and found it is far less inevitable than astronomers had previously suspected.
“We have the most comprehensive study of this problem today that actually folds in all the observational uncertainties,” said Till Sawala, astronomer at the University of Helsinki in Finland and lead author of the study, which appears today in the journal Nature Astronomy.
His team includes researchers at Durham University, United Kingdom; the University of Toulouse, France; and the University of Western Australia. They found that there is approximately a 50-50 chance of the two galaxies colliding within the next 10 billion years. They based this conclusion on computer simulations using the latest observational data.
These galaxy images illustrate three possible encounter scenarios between our Milky Way and the neighboring Andromeda galaxy. Top left: Galaxies M81 and M82. Top right: NGC 6786, a pair of interacting galaxies. Bottom: NGC 520, two merging galaxies. Science: NASA, ESA, STScI, DSS, Till Sawala (University of Helsinki); Image Processing: Joseph DePasquale (STScI) Sawala emphasized that predicting the long-term future of galaxy interactions is highly uncertain, but the new findings challenge the previous consensus and suggest the fate of the Milky Way remains an open question.
“Even using the latest and most precise observational data available, the future of the Local Group of several dozen galaxies is uncertain. Intriguingly, we find an almost equal probability for the widely publicized merger scenario, or, conversely, an alternative one where the Milky Way and Andromeda survive unscathed,” said Sawala.
The collision of the two galaxies had seemed much more likely in 2012, when astronomers Roeland van der Marel and Tony Sohn of the Space Telescope Science Institute in Baltimore, Maryland published a detailed analysis of Hubble observations over a five-to-seven-year period, indicating a direct impact in no more than 5 billion years.
“It’s somewhat ironic that, despite the addition of more precise Hubble data taken in recent years, we are now less certain about the outcome of a potential collision. That’s because of the more complex analysis and because we consider a more complete system. But the only way to get to a new prediction about the eventual fate of the Milky Way will be with even better data,” said Sawala.
100,000 Crash-Dummy Simulations
Astronomers considered 22 different variables that could affect the potential collision between our galaxy and our neighbor, and ran 100,000 simulations called Monte Carlo simulations stretching to 10 billion years into the future.
“Because there are so many variables that each have their errors, that accumulates to rather large uncertainty about the outcome, leading to the conclusion that the chance of a direct collision is only 50% within the next 10 billion years,” said Sawala.
“The Milky Way and Andromeda alone would remain in the same plane as they orbit each other, but this doesn’t mean they need to crash. They could still go past each other,” said Sawala.
Researchers also considered the effects of the orbits of Andromeda’s large satellite galaxy, M33, and a satellite galaxy of the Milky Way called the Large Magellanic Cloud (LMC).
“The extra mass of Andromeda’s satellite galaxy M33 pulls the Milky Way a little bit more towards it. However, we also show that the LMC pulls the Milky Way off the orbital plane and away from Andromeda. It doesn’t mean that the LMC will save us from that merger, but it makes it a bit less likely,” said Sawala.
In about half of the simulations, the two main galaxies fly past each other separated by around half a million light-years or less (five times the Milky Way’s diameter). They move outward but then come back and eventually merge in the far future. The gradual decay of the orbit is caused by a process called dynamical friction between the vast dark-matter halos that surround each galaxy at the beginning.
In most of the other cases, the galaxies don’t even come close enough for dynamical friction to work effectively. In this case, the two galaxies can continue their orbital waltz for a very long time.
The new result also still leaves a small chance of around 2% for a head-on collision between the galaxies in only 4 to 5 billion years. Considering that the warming Sun makes Earth uninhabitable in roughly 1 billion years, and the Sun itself will likely burn out in 5 billion years, a collision with Andromeda is the least of our cosmic worries.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble 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 and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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Milky Way and Andromeda Encounters
This selection of images of external galaxies illustrates three encounter scenarios between our Milky Way and the neighboring Andromeda galaxy. Top left: Galaxies M81 and M82. Top right: NGC 6786, a pair of interacting galaxies. Bottom: NGC 520, two merging galaxies.
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Last Updated Jun 02, 2025 Editor Andrea Gianopoulos Location NASA Goddard Space Flight Center
Contact Media Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov
Ray Villard
Space Telescope Science Institute
Baltimore, Maryland
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Sols 4525-4526: The Day After Groundhog Day (Between Ghost Mountain and Texoli, Headed South)
NASA’s Mars rover Curiosity acquired this image showing ChemCam/Mastcam targets “Breeze Hill” and “Laguna Mountain,” together with a rover wheel planted firmly on the Martian surface. Curiosity captured the image using its Left Navigation Camera on April 27, 2025 — Sol 4523, or Martian day 4,523 of the Mars Science Laboratory mission — at 13:23:32 UTC. NASA/JPL-Caltech Written by Lucy Lim, Planetary Scientist at NASA Goddard Space Flight Center
Earth planning date: Monday, April 28, 2025
Curiosity is back on the road! For sols 4525 and 4526, we have an isolated nominal plan in which the communication pass timing works out in such a way that the rover can fit in fully targeted science blocks on both sols rather than just the first sol. So in this power-hungry Martian winter season, we’re in a good position to take advantage of the power saved up during the missed uplink.
The weekend drive went well and delivered the rover into a stable, arm-work-compatible position in a workspace with rock targets that we could brush with the DRT. Happy days! The DRT/APXS/MAHLI measurements will bring us geochemical and rock texture data from local bedrock blocks “Bradshaw Trail” and “Sweetwater River.” Further geochemical information will come from the ChemCam LIBS rasters on a more coarsely layered target, “Breeze Hill,” and an exposed layer expressing both polygonal features and a vein or coating of dark-toned material, “Laguna Mountain.”
Long-distance imaging with the ChemCam RMI included a mosaic to add to our coverage of the boxwork sedimentary features of the type Curiosity will soon be exploring in situ. A second RMI mosaic was planned to cover a truncated sedimentary horizon on the Texoli butte that may provide further evidence of ancient aeolian scouring events. Meanwhile, the “Morrell Potrero” Mastcam mosaic will provide some detail on the base of the boxwork-bearing “Ghost Mountain” butte and on a ridge nearby. In the drive direction, the “Garnet Peak” mosaic will capture some potentially new rock textures and colors in the upcoming strata.
Nearer-field imaging in the plan includes Mastcam documentation of some troughs that provide evidence for sand and dust movement in response to the modern aeolian environment. Additionally Mastcam mosaics went to “Breeze Hill” (covering the LIBS target) and “Live Oak” to document variations in bedding, color, and texture in the nearby bedrock.
A few observations of the modern environment were scheduled for the afternoon: a phase function sky survey to look for scattered light from thin water-ice clouds and a separate set of cloud altitude observations.
Finally, a Mastcam documentation image was planned for the AEGIS LIBS target from the weekend plan! This reflects an update to the rover’s capability in which the AEGIS target can be determined and downlinked in time for the decisional downlink pass, so that we know where to look for it during the next planning cycle.
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Last Updated Apr 30, 2025 Related Terms
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A SpaceX Falcon 9 rocket stands vertical on Tuesday, Feb. 25, 2025, at Launch Complex 39A at NASA’s Kennedy Space Center ahead of Intuitive Machines’ IM-2 mission as part of the agency’s Commercial Lunar Payload Services initiative and Artemis campaign. SpaceX Sending instruments to the Moon supports a growing lunar economy on and off Earth, and the next flight of NASA science and technology is only days away. NASA’s CLPS (Commercial Lunar Payload Services) initiative is a lunar delivery service that sends NASA science and technology instruments to various geographic locations on the Moon using American companies. These rapid, cost-effective commercial lunar missions at a cadence of about two per year improve our understanding of the lunar environment in advance of future crewed missions to the Moon as part of the agency’s broader Artemis campaign.
Of the 11 active CLPS contracts, there have been three CLPS launches to date: Astrobotic’s Peregrine Mission One, which collected data in transit but experienced an anomaly that prevented it from landing on the Moon; Intuitive Machines’ IM-1 mission, which landed, tipped over, and operated on the lunar surface; and Firefly Aerospace’s Blue Ghost Mission One that is currently enroute and scheduled to land in early March 2025. The CLPS contract awards cover end-to-end commercial payload delivery services, including payload integration, launch from Earth, landing on the surface of the Moon, and mission operations.
NASA’s fourth CLPS flight is from Intuitive Machines with their IM-2 mission. The IM-2 mission is carrying NASA science and technology instruments to Mons Mouton, a lunar plateau just outside of 5 degrees of the South Pole of the Moon, closer to the pole than any preceding lunar mission.
Scheduled to launch no earlier than Wednesday and land approximately eight days later, Intuitive Machines’ Nova-C lander, named Athena, will carry three NASA instruments to the lunar South Pole region – the Polar Resources Ice Mining Experiment-1 (PRIME-1) suite and the Laser Retroreflector Array (LRA).
The PRIME-1 suite consists of two instruments, the TRIDENT drill (The Regolith Ice Drill for Exploring New Terrain) and MSolo (Mass Spectrometer observing lunar operations), which will work together to extricate lunar soil samples, known as regolith, from the subsurface and analyze their composition to further understand the lunar environment and gain insight on potential resources that can be extracted for future examination.
The meter-long TRIDENT drill is designed to extract lunar regolith, up to about three feet below the surface. It will also measure soil temperature at varying depths below the surface, which will help to verify existing lunar thermal models that are used for ice stability calculations and resource mapping. By drilling into the lunar regolith, information is gathered to help answer questions about the lunar regolith geotechnical properties, such as soil strength, both at the surface and in the subsurface that will help inform Artemis infrastructure objectives. The data will be beneficial when designing future systems for on-site resource utilization that will use local resources to create everything from landing pads to rocket fuel. The lead development organization for TRIDENT is Honeybee Robotics, a Blue Origin Company.
The MSOLO instrument is a mass spectrometer capable of identifying and quantifying volatiles (or gasses that easily evaporate) found at or beneath the lunar surface, including– if it’s present in the regolith within the drill’s reach – water and oxygen, brought to the surface by the TRIDENT drill. This instrument can also detect any gases that emanate from the lander, drilling process, and other payloads conducting operations on the surface. Using MSolo to study the volatile gases found on the Moon can help us understand how the lander’s presence might alter the local environment. The lead development organization is INFICON of Syracuse, New York, in partnership with NASA’s Kennedy Space Center in Florida.
NASA’s LRA is a collection of eight retroreflectors that enable precision laser ranging, which is a measurement of the distance between the orbiting or landing spacecraft to the reflector on the lander. The LRA instrument is passive, meaning it does not power on. It will function as a permanent location marker on the Moon for decades to come, similar to its predecessors. The lead development organization is NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
In addition to the CLPS instruments, two technology demonstrations aboard IM-2 were developed through NASA’s Tipping Point opportunity. These are collaborations with the agency’s Space Technology Mission Directorate and industry that support development of commercial space capabilities and benefit future NASA missions.
Intuitive Machines developed a small hopping robot, Grace, named after Grace Hopper, computer scientist and mathematician. Grace will deploy as a secondary payload from the lander and enable high-resolution imaging and science surveying of the lunar surface, including permanently shadowed craters around the landing site. Grace is designed to bypass obstacles such as steep inclines, boulders, and craters to cover a lot of terrain while moving quickly, which is a valuable capability to support future missions on the Moon and other planets, including Mars.
Nokia will test a Lunar Surface Communications System that employs the same cellular technology here on Earth. Reconceptualized by Nokia Bell Labs to meet the unique requirements of a lunar mission, this tipping point technology aims to demonstrate proximity communications between the lander, a Lunar Outpost rover, and the hopper.
Launching as a rideshare alongside the IM-2 mission, NASA’s Lunar Trailblazer spacecraft also will begin its journey to lunar orbit where it will map the distribution of water – and other forms of water – on the Moon.
Future CLPS flights will continue to send payloads to the near side, far side, and South Pole regions of the Moon where investigations and exploration are informed by each area’s unique characteristics. With a pool of 13 American companies under CLPS, including a portfolio of 11 lunar deliveries by five vendors sending more than 50 individual science and technology instruments to lunar orbit and the surface of the Moon, NASA continues to advance long-term exploration of the Moon, and beyond to Mars.
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