Atmospheric gas around galaxies (orange) fuels the formation of stars within galaxies (white at end of video)
Source: Illustris TNG Team
Lynx is a revolutionary X-ray observatory that will transform our understanding of galactic atmospheres and how they are connected to black holes.
Background Image: A science-based artistic visualization of the region near a black hole’s event horizon.
Source: Niko Maizuradze for the Lynx Team.
Now part of a unified vision for NASA’s New Great Observatories, Lynx was one of the large mission concepts considered by the 2020 Decadal Survey in Astronomy & Astrophysics.
Background image: A simulated galactic wind erupting from the right and blowing to the left.
Source: Evan Schneider
The Hidden Cosmos
Galactic atmospheres are just one part of the Hidden Cosmos that Lynx will unveil. While the hottest realms of the luminous Universe account for most of its gas mass across cosmic time, those realms cannot be seen with ground-based telescopes. Gas hotter than a few thousand degrees shines brightest in X-rays, which cannot penetrate Earth’s atmosphere and reach the ground. Lynx is therefore a space-based observatory.
Direct X-ray observations of those crucial but otherwise invisible regions will reveal cosmic structure in the process of becoming galaxies, stars, and planets. They will also provide essential insights into how black hole eruptions and supernova explosions sculpt cosmic change.
From the dynamos of infant suns to the vast web of dark matter giving shape to the cosmic expanse, X-ray emitting hot gas signals the most fundamental actions of nature’s unseen instruments. Galaxy evolution depends critically on the feedback loops that connect supernovae and black holes to the hot-gas reservoirs around galaxies. And the universe’s most powerful eruptions are fueled by the hot disks of doomed gas spiraling around supermassive black holes.
If the story of discovery has been one of expansion into unknown spaces, Lynx can write the next volume with the X-ray signals it collects from the Hidden Cosmos. In all aspects, Lynx is a new Great Observatory poised to initiate a novel epoch in our understanding of nature. From the shining poles of Jupiter to black holes at the edge of time, it will expand every border of the future scientific landscape, with capabilities broad enough to answer questions we have not even yet thought to ask.
To achieve those goals, Lynx will carry revolutionary instrumentation into space, making it a transformative X-ray observatory aboard a proven, tested, and simple spacecraft. It is the most powerful X-ray observatory ever designed. It will carry enough fuel to power more than two decades of operation. And we are ready to build it right now.
Galaxy Formation & Feedback
Galaxy formation begins with the gravitational attraction of dark matter (upper left panel), as shown the simulation above. After forming a web-like structure, dark matter clumps attract other dark matter clumps. As those clumps assemble into larger structures, their combined gravity pulls in the surrounding atmospheric gas and heats it up. The hottest gaseous regions then glow in X-rays (lower right panel), making them visible with Lynx.
Stars begin to form where the hot gas is able to cool, producing warm gas clouds that cool further to become cold ones (lower left panel). After those stars form (upper right panel), they continue to orbit within the largest clumps of dark matter.
Violent feedback processes soon push back on the hot gas, as supernovae start to explode and supermassive black holes begin to grow. X-ray observations provide our best views of how those violent eruptions disrupt the atmospheres of galaxies, slowing and sometimes even halting the supply of gas for star formation.
Only Lynx will be capable of mapping this hot gas around galaxies like the Milky Way and elsewhere in the Cosmic Web of dark matter.
Lynx is designed to characterize all these modes of energetic feedback in unprecedented detail. Its essential observations will require mapping of low surface brightness X-ray emission from galactic atmospheres, including high-resolution spectroscopy with arc-second angular precision, along with high-resolution spectroscopy of active galactic nuclei behind those atmospheres, to detect X-ray absorbing gas components not bright enough to otherwise be seen.
All of those essential capabilities will be unique to Lynx.
Simulation: Benjamin Oppenheimer (University of Colorado, RMACC Summit Supercomputer)
Visualization: Adrien Thob, Thor Metzinger, Grant Tremblay, Suphawit Duangphumek, Timothy Dunn
A Simulated Lynx Observation
This movie shows how Lynx observations will reveal the physics of galactic atmospheres. On the left is a gas-phase diagram depicting how gas density is related to gas temperature in the TNG50 supercomputer simulation of galaxy formation. On the right is a map of the hot gas in that simulation. A scale bar indicates a distance of 10 Megaparsecs (approximately 30 million light-years).
Much of the gas in the simulation “box” is at a temperature of several million degrees (between $10^6$ and $10^7$ K), making it hot enough to emit X-rays. It can therefore be seen “in emission.” Some of the hot gas is not quite dense enough to emit detectable X-rays but can still absorb X-rays passing through it, making it detectable “in absorption.” Somewhat cooler atmospheric gases (shown in blue and green) interact with ultraviolet and visible light detectable with UV/Optical space telescopes. The most diffuse, low-density gas, known as the Warm-Hot Intergalactic Medium (WHIM), is the most difficult to detect.
Inset images on the right are zoomed in views of a galaxy similar to the Andromeda Galaxy (M31), which is the nearest large spiral galaxy to our Milky Way. They show the distributions of atmospheric gases detectable with X-ray and UV/Optical telescopes across a region 300 kiloparsecs (about 1 million light-years) in size.
Simulation: Rainer Weinberger & the Illustris TNG Team,
Visualization: Grant Tremblay & the Lynx Team
The Lynx Legacy Field
One of the most revolutionary ideas proposed by the Lynx team is an observation called the Lynx Legacy Field. To make that observation, Lynx would spend 10 Megaseconds (about four months) surveying a region of the sky 10 square degrees in size.
The workhorse camera would be the High Definition X-ray Imager (HDXI), which has a “footprint” on the sky approximately 1/3 of a degree across, slightly smaller than the apparent size of the Moon as viewed from Earth. Each exposure would take 100 kiloseconds (about a day). The entire survey would be a mosaic of a hundred such exposures.
Choosing a region of the sky centered on a massive galaxy cluster would reveal not only an unprecedented view of a galaxy cluster’s atmosphere. It would also reveal the diffuse hot gas tracing a previously unseen network of dark matter filaments extending more than 10 Megaparsecs (30 million light-years) from the cluster.
In the seemingly dark spaces between those filaments would be multitudes of other faint but detectable X-ray sources, including the accretion disks around brand-new black holes near the edges of our observable universe and hot atmospheres around the earliest generations of galaxy clusters and groups.
Visualization: Grant Tremblay, John ZuHone, Benjamin Oppenheimer & Alexey Vikhlinin for the Lynx Team
