Free Astronomy Magazine May-June 2021

32 MAY-JUNE 2021 ASTRO PUBLISHING thought that the M87 jet was the result of a black hole, even though it nor any other black hole had been seen directly. For decades, black holes had only been a theory supported by indi- rect observational evidence, such as through their gravi- tational influence and by the jets of matter ejected at very high speeds from galac- tic nuclei. It is not easy to record this structure using the equipment available at OLA, not so much for the weakness and thinness of the jet, but mainly due to the great brightness of the M87 core, which saturates the pixels imaging the cen- ter of the galaxy, hiding the fine details in that region. In the images and in the first treatments, the plasma jet appears only as a small swelling or spike that only indicated its faint presence or, perhaps, showed it to be just a bit more prominent. The integration times had to be calculated carefully. Likewise, the choice of fil- ters to be used and their characteristics were impor- tant − we were trying to record true color using the LRGB color palette. Subse- quently, we verified that the jet, being bluish, would have required an increase in the in- tegrations of the blue filter (B), but ignorance of this made us assign identical exposure times to each fil- ter. We also did exposures in H α , knowing (or almost knowing) that they would not provide any extra information. As they would likely worsen our signal-to-noise ratio, which became evident in the pro- cessing, we ultimately discarded the H α data. T he jet of M87. Forced processing to isolate the plasma jet from the galaxy core makes the field stars appear with strange edges and halos. 10” f/3.9 Newtonian telescope, SBIG ST-8300M CCD camera, 8.3 megapixel KAF-8300 sensor, 5.4x5.4 µ (3326x2504 pixels), Ger- man equatorial mount EQ-8. [M. Sánchez (SAG), A. Porcel (SAG/OLA)] The images were acquired with the help of the software programs Maxim DL, Astrotortilla, EQMOD and Cartes du Ciel. Each of the pro- duced FITS (Flexible Image Trans- port System) files was initially processed with Avis FITS Viewer (AvisFV) to reduce the brightness of the galaxy’s core until the plasma jet was exposed. Image stacking was performed with DeepSkyStacker (DSS), including lu- minance (L) in the red (R+L) channel and independent green (G) and blue (B) channels. The color (RGB) mon- tage was done with Photoshop, where it was reworked to recali- brate color, brightness and contrast. The IRIS program was used for the spatial measurements of the jet. The final image of the M87 field is an LRGB stacking in the following proportions: L 3×300", R 3×300", G 3×300", B 3×300"; 12 shots of 300