17782( 3) - 22-Jul-2025 21:14:03 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17782 Version: 3 Check-in Time: 22-Jul-2025 21:14:03 STScI Edit Number: 0 Title A First Attempt to Detect Extragalactic Antimatter: Positronium Lyman alpha toward M31* ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Jeremy Darling University of Colorado at Boulder Y ------------------------------------------------------------------------------------ Abstract We propose to attempt the first direct detection of antimatter outside the Galaxy by observing the positronium Lyman-alpha transition toward M31*. The existence of antimatter in the form of positrons has been observed in the Galaxy via 511 keV annihilation photons for half a century, but the astrophysical engines producing the positrons have yet to be identified. Numerous plausible sources of positrons have been proposed, some of which are distributed and some of which are pointlike such as massive black holes, stellar-mass black holes, and compact X-ray binaries. Studies of the annihilation gamma-ray spectrum show that nearly all annihilation events are preceded by the formation of an electron-positron bound state called Positronium (Ps), a hydrogen-like "atom" where the proton is replaced by the positron. Positronium has quantum transitions with half the energy of hydrogen: its Lyman alpha line has a wavelength 243 nm. There will therefore be Ps "recombination" emission lines that precede annihilation. These are faint but within the reach of HST, and ground-based observations have thus far been unable to adequately remove terrestrial atmospheric spectral features, despite custom-built spectrometers. We propose to expand the study of the sources of antimatter beyond the Galaxy by observing M31* in the Ps Lyman-alpha transition. Successful detection will provide important insight into positron production mechanisms and the general physics of high-energy phenomena. Theory alone has so far been unable to identify the dominant mechanism for antimatter production. ------------------------------------------------------------------------------------ Observations Description ------------------------ The plan is to obtain a spectrum of M31* in the Ps Lyman alpha transition at 243 nm. We split the observations into two visits of 3 orbits each, and spread the four FP-POS settings over the two visits (six orbits). For each visit and orbit, we do two COS exposures with G230L, TIME-TAG mode, wavelength 3360 A, placing Segment A on the 243 nm Ps transition. The M31* nuclear environment is extended in the NUV and will not reward an aquisition obervation, even for peak-finding. We use the radio coordinates for M31*, which are good to less than 0.25". The default pointing by HST will be perfectly adequate to obtain a spectrum of the nuclear region to search for antimatter. ------------------------------------------------------------------------------------ 17782( 3) - 22-Jul-2025 21:14:03 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M31STAR GALAXY, NUCLEUS RA=00H42M44.3440S +/- 0.25", J2000 V = 12 The HST-measured FUV flux at DEC=+41D16'8.54" +/- 0.25" 2000 A is 1e-15 erg/s/cm^2/A; we use this to estimate the 2430 A continuum. Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17782( 3) - 22-Jul-2025 21:14:03 - [ 3] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=1 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=1 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=1 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=2 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=2 1 1200 S G see below (1245 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=2 1 1200 S G see below (1245 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31STAR 1 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G M31STAR 2 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G M31STAR 3 COS/NUV TIME-TA PSA G230L 3360 none none none none 2 1244.0 S G M31STAR 4 COS/NUV TIME-TA PSA G230L 3360 none none none none 2 1244.0 S G M31STAR 5 COS/NUV TIME-TA PSA G230L 3360 none none none none 3 1245.0 S G M31STAR 6 COS/NUV TIME-TA PSA G230L 3360 none none none none 3 1245.0 S G 17782( 3) - 22-Jul-2025 21:14:03 - [ 4] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=3 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=3 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=3 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=4 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=4 1 1200 S G see below (1245 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=4 1 1200 S G see below (1245 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31STAR 1 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G M31STAR 2 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G M31STAR 3 COS/NUV TIME-TA PSA G230L 3360 none none none none 2 1244.0 S G M31STAR 4 COS/NUV TIME-TA PSA G230L 3360 none none none none 2 1244.0 S G M31STAR 5 COS/NUV TIME-TA PSA G230L 3360 none none none none 3 1245.0 S G M31STAR 6 COS/NUV TIME-TA PSA G230L 3360 none none none none 3 1245.0 S G 17782( 3) - 22-Jul-2025 21:14:03 - [ 5] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=2 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31STAR COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1193, FP-POS=2 1 1200 S G see below (1244 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31STAR 1 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G M31STAR 2 COS/NUV TIME-TA PSA G230L 3360 none none none none 1 1244.0 S G 17782( 3) - 22-Jul-2025 21:14:03 - [ 6] Summary Form for Proposal 17782 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1193, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names M31STAR ------------------------------------------------------------------------------------------------------------------------------------