{"id":4753,"date":"2026-06-18T19:09:46","date_gmt":"2026-06-18T17:09:46","guid":{"rendered":"https:\/\/sphe.astro.cz\/v838-mon-how-we-turned-hubble\/"},"modified":"2026-08-28T12:37:56","modified_gmt":"2026-08-28T10:37:56","slug":"v838-mon-how-we-turned-hubble","status":"publish","type":"page","link":"https:\/\/sphe.astro.cz\/en\/v838-mon-how-we-turned-hubble\/","title":{"rendered":"V838 Mon \u2013 How We “Turned” Hubble"},"content":{"rendered":"\t\t
\n\t\t\t\t
\n\t\t\t\t\t
\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

How on February 2, 2002, four Czech amateur observers from our section captured the second outburstof an unknown object in the constellation Monoceros \u2014 and thereby triggered a campaign that led all the way to the Hubble Space Telescope.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

\n\t\t\t\t\t
\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t\t\t\t
\n\t\t\t\t\t\t\t\t\t\t\"\"\t\t\t\t\t\t\t\t\t\t\t
Light echo of V838 Mon (Credit: NASA, ESA and the Hubble Heritage Team (STScI\/AURA)<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

Saturday, February 2, 2002. After weeks of overcast skies, finally frost and clear weather. Ladislav \u0160melcer at the Vala\u0161sk\u00e9 Mezi\u0159\u00ed\u010d\u00ed Observatory points a CCD camera at the star V838 in the constellation Monoceros. A peculiar object, discovered a month earlier in Australia by Nicholas Brown, which until then almost no one in the Czech Republic had measured. At 7:47 PM CET, \u0160melcer’s photometry shows 8.17 magnitude. That is nearly three magnitudes less than previous observations \u2014 and with stars, the lower the magnitude, the brighter it is. V838 Mon brightened about forty times within a few days. \u0160melcer picks up the phone. Everything is just beginning \u21e3 <\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

\n\t\t\t\t\t
\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\"\"\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t

One Phone Call and a Campaign is Born<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

He calls Lubo\u0161 Br\u00e1t in Pec pod Sn\u011b\u017ekou \u2014 also a long-time member of the section, also an observer of variable stars. Br\u00e1t is just preparing his telescope for the constellation Monoceros. He only needs to point it. At 8:19 PM, he confirms visually. He immediately calls Ond\u0159ej Pejcha and Petr Sobotka at the Brno Observatory \u2014 also members of the section, also at their telescopes. Paradoxically, they were the first to have V838 Mon, which they considered a very interesting object, in their telescope. That was as early as 6:45 PM, but due to the overexposure of the first image and the subsequent filter change, they did not immediately recognize the ongoing changes. Then Br\u00e1t runs home and at 8:29 PM sends a message to the international astronomical conference VSNET. That message starts a worldwide observation campaign. Within a few hours, people from literally all over the world join in observing V838 Mon. Meanwhile, in Brno, Pejcha and Sobotka start rapid photometry with an exposure every 20 seconds. At 11:15 PM, they send a report to the International Astronomical Union Circular. An hour later, they look at the plotted light curve and cry out in amazement \u2014 the star is rising at a rate of 0.1 magnitude per hour. Thus, it doubles its brightness every seven hours. <\/p>

During that night, three other Czech observers from our section sent their independent observations to VSNET: Peter Dubovsk\u00fd, Kamil Hornoch, and Luk\u00e1\u0161 Kr\u00e1l. At that time, several other observers and groups around the world also captured the brightening – this is not an exception for such dramatic events. However, the significance of a discovery is not decided by who was first by a few hours. It is decided by rapid confirmation, systematic monitoring, and interpretation. And that is exactly where our observers played their part. <\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

\n\t\t\t\t\t
\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t

Hubble, the Light Echo, and Something Entirely New<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

V838 Mon reached a maximum of V = 6.66 magnitude on February 6, 2002. Then it began to fade rapidly. In mid-February, however, what definitively made this object famous appeared around it \u2014 a light echo. The star’s flash gradually illuminated the dust in its vicinity, which until then could not be distinguished from the background. NASA therefore turned the Hubble Space Telescope toward V838 Mon.<\/strong> A series of images was created that today rank among the most famous astronomical images of the modern era (Bond et al., Nature 422, 2003). You can find an animation of the expanding echo in the video at the very beginning of this website \u2014 and now you know why it says underneath that we had a hand in it.From a physical perspective, it turned out that V838 Mon is neither a classical nova (from a white dwarf in a binary system) nor a supernova (which tears the star apart). It reached a maximum luminosity roughly six hundred thousand times greater than the Sun, and its spectrum changed so dramatically over a few weeks that it did not fit into any previously known category of eruptive objects. In the following months, the star cooled so much that its spectrum corresponded to type L – a class otherwise reserved for brown dwarfs, yet it still shone as brightly as roughly one hundred thousand Suns. An object with the temperature of a dwarf and the luminosity of a supergiant. It was something new. The explanation that is considered most likely today was proposed in 2006 by Polish astronomer Romuald Tylenda and Israeli Noam Soker (A&A 451, 223). According to them, the eruption was the result of a stellar merger \u2014 a collision of a B-type main-sequence star with a mass of roughly eight Suns and a young stellar object with a mass of approximately four-tenths of the Sun. V838 Mon became the prototype of a new class of eruptive variables called luminous red novae (luminous red novae<\/em>) and, along with the star V1309 Scorpii, which erupted six years later, remains one of the fundamental objects of this category today. Hubble, ALMA, infrared interferometers, and dozens of other observatories have returned to V838 Mon, many repeatedly. The eruption that Ladislav \u0160melcer discovered just before eight in the evening in Vala\u0161sk\u00e9 Mezi\u0159\u00ed\u010d\u00ed remains one of the best-documented cosmic events of the 21st century. <\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

\n\t\t\t\t\t
\n\t\t
\n\t\t\t\t
\n\t\t\t\t\t

Why We Are Telling This Story<\/h2>\t\t\t\t<\/div>\n\t\t\t\t
\n\t\t\t\t\t\t\t\t\t

\u0160melcer, Br\u00e1t, Pejcha, and Sobotka did nothing extraordinary that night. They did what they did anddo many nights a year: they observed, measured, compared, and communicated. From the perspective of the variable starsection, it was almost routine. But a routine that has the quality of sometimes triggeringan avalanche. A scientific avalanche. <\/p>

For the sake of completeness, let us add that Ond\u0159ej Pejcha, who was doing one of his firstindependent nights with CCD technology in Brno that night, is now an associate professor of astrophysics at the Faculty of Mathematics and Physicsof Charles University (his research team, supported by two European ERC grants, isamong other things dealing precisely with stellar mergers \u2014 the mechanism behind V838 Mon).Petr Sobotka worked for many years at the Astronomical Institute of the Czech Academy of Sciences and is now the secretary of the CzechAstronomical Society. Ladislav \u0160melcer remains a long-time pillar of our section forthe observation program focused primarily on eruptive variable stars. Lubo\u0161 Br\u00e1tcurrently remains a member of the section but is more involved in other activities. <\/p>

All of this can happen again \u2014 maybe tomorrow night, maybe next year. And to observevariable stars today, you don’t need mega-scientific equipment. A telescope, a detector,and the will are enough. If you want to be part of it, our doors are open to you. <\/p>