At around this time, M87’s true distance of 55 to 60 million light-years became apparent, letting us pin its diameter at 120,000 light-years, which is similar to the size of our galaxy. Except that M87’s far greater density, and the fact that its 2.7 trillion members form a voluminous ball rather than a disk, puts it out of our population league. Recent photos show fainter outer layers that extend much farther, making its true size in our sky more like ½°, the same as the Full Moon. This forced a major recent revision of its width to 500,000 light-years. And just this year, studies reveal that M87 likely swallowed an entire other galaxy in the last billion years.
In 1954, M87 was identified as the visual object corresponding to an intense point-like source of celestial radio noise found in 1947, named Virgo A. Later, in 1965 and 1967, when rocket-borne X-ray detectors became available, observers saw M87 as a powerful source of those emissions as well, whose filaments extend far beyond the visible jet for an amazing 100,000 light-years. Messier 87 also creates extremely strong gamma-ray emissions, the most powerful electromagnetic energy of all.
Naturally, when the Hubble Space Telescope launched, M87 became a prime focus of its investigations — especially that odd jet shooting westward from its center, which Hubble showed to be violently roiling and boiling. A second, much smaller jet also was discovered emanating from the exact opposite side of the galaxy’s supermassive black hole. A knot in the main jet, named HST-1, periodically monitored by the Hubble Space Telescope and the Chandra X-ray Observatory, has over a relatively recent four-year period mysteriously grown 50 times brighter.