The Black Hole Explorer (BHEX) is a space-VLBI mission that will extend the Event Horizon Telescope into space. The cryogenic receivers must be cooled down to 4.5K. A cryogenic system consisting of two Stirling cryocoolers and a Joule-Thomson cooler has been explored which consists of a 20K and a 4.5K cold stage in order to cool a combined heat load of approximately 250mW. The integration challenges of the cryocooling system with the receivers and broader instrument are explored, where power, mass, and thermal challenges require careful considerations and trade-off. This study presents a feasible cryocooling design that reaches the cold temperature requirements of the BHEX instrument.

The Black Hole Explorer (BHEX), is an orbiting, multi-band, millimeter radio-telescope, in hybrid combination with millimeter terrestrial radio-telescopes, designed to discover and measure the thin photon ring around the supermassive black holes M87* and Sgr A*. In order to guide the mission design for the BHEX instruments, this paper explores various aspects of the photon ring, like the spin-induced changes to its shape, or the intricate flow of light around a spinning black hole, by tracking, through visual simulations, photons as they course along geodesics. Ultimately, the aim of these visualizations is to advance the foundational aims of the EHE instrument, and through this experiment to articulate spacetime geometry via the photon ring.

The photon ring is a narrow ring-shaped feature (predicted by general relativity, but not yet observed) that appears in black hole images. It is caused by the extreme bending of light within a few Schwarzschild radii of the event horizon and provides a direct probe of the unstable bound photon orbits of the Kerr black hole geometry. The precise shape of the observable photon ring is remarkably insensitive to the details of the astronomical source and can therefore be used as a precise probe of strong-field gravity. The Black Hole Explorer (BHEX) is a proposed space-based experiment targeting the supermassive black holes M87* and Sgr A* with radio-interferometric observations at frequencies of 86 through 345 GHz and from an orbital distance of ~40,000km. We forecast that its design will enable a measurement of the photon rings around M87* and Sgr A* and confirm the Kerr nature of these two sources.

We present a baseline science operations plan for the Black Hole Explorer (BHEX), a space mission concept aiming to confirm the existence of the predicted sharp “photon ring” resulting from strongly lensed photon trajectories around black holes, as predicted by general relativity, and to measure its size and shape to determine the black hole's spin. The BHEX radio antenna will co-observe with a ground-based very long baseline interferometric (VLBI) array, providing unprecedented high resolution with the extension to space that will enable photon ring detection and studies of active galactic nuclei. Here we outline the concept of operations for the hybrid observatory coordinating both a VLBI network and an optical downlink terminal network, the available observing modes, the proposal and observation planning process, and data delivery to achieve the BHEX mission goals and meet mission requirements.

We describe the baseline design of the science instrument for the Black Hole Explorer (BHEX), a space very long baseline interferometry (VLBI) mission concept currently in the formulation phase. BHEX will study supermassive black holes to understand fundamental physics, black hole jets, and the growth of black holes in galaxies. By co-observing with ground radio telescopes, BHEX will achieve 3-5 micro-arcsecond resolution from a distance of ~40,000 km. Observations will be conducted in two simultaneous bands between 80-350GHz, using an on-board low-power, low-mass ultra-stable oscillator as the master frequency reference, and the digitized data will be transmitted to the ground through an ultra-wide bandwidth laser downlink.

The Black Hole Explorer: (BHEX) is a space mission to image radio emissions of black holes by expanding both the baseline and time resolution of Very Long Baseline Interferometry (VLBI). This involves integrating a space telescope into an array of ground telescopes, such as the Event Horizon Telescope (EHT). Ultimately, the EHE will enable transformative science and the mission goals are well aligned with the Astro 2020 Decadal Survey. The EHE mission concept study was designed with three major stages: (1) a Science Study which articulates plausible goals and objectives (2) an Engineering Study which articulates overall feasi- bility and technological readiness and (3) a Mission Architecture Study which combines the results of the previous studies to match achievable science goals and objectives with feasible engineering to yield a plausible mission architecture. This paper review the initial steps taken under stage two of the EHE project.

The Black Hole Explorer (BHEX) is a next-generation space very long baseline interferometry (VLBI) mission concept that will extend the ground-based Event Horizon Telescope into space. The Japanese community is poised to make major contributions to the mission, ranging from science to mission-critical instrumentation. Here we present the Japanese vision for the mission. A potential major technical contribution is providing key components for its sensitive tri-band receiving system, including SIS mixers at 230 and 345 GHz and a space-qualified multi-stage 4.5K cryocooler similar to that on JAXA’s Hitomi and XRISM satellites. The Japanese community envisions broad science cases spanning from various black hole physics/astrophysics explored with VLBI to molecular universe explored by the potential single-dish observing mode at radio frequencies to be explored for the first time with the BHEX mission.

We present the motivation and vision for the Black Hole Explorer (BHEX), a mission that will extend submillimeter Very Long Baseline Interferometry (VLBI) to space. BHEX, currently under formulation for a NASA Small Explorer mission, will discover and measure the bright and narrow “photon ring” that is predicted to exist in images of black holes, will reveal the processes that drive supermassive black hole creation and growth, and will connect supermassive black holes to their relativistic jets.

Around the horizon of a black hole, an edge of the universe, light is captured, spun into orbit by the black hole’s powerful gravitational pull. Lying within the orange donut in the famous first image of a black hole, this “photon ring” would be a prize to measure—it would reveal the nature of spacetime itself, directly, near the horizon. Indeed, the shape of this pure ring of light tells everything about the black hole. With the stakes this high, a new collaboration—physicists, astronomers, engineers from around the world—has formed to loft a spacecraft that capture the photon ring. We are at the beginning of what is probably a ten-year effort—this is a film about the start of that adventure.

A film by Peter Galison, Michael Johnson, and Chyld King