Author Archives: karlmenten

CRC 956 funded for another four years

Funding of the Collaborative Research Centre (CRC) 956, entitled „Conditions and Impact of Star Formation – Astrophysics, Instrumentation and Laboratory Research“, has just been extended for another period of 4 years. CRC 956 explores basic star-formation processes and with that is contributing to worldwide exchange of extended knowledge between researchers. It is jointly run by the I. Physikalische Institut der Universität Köln, the Argelander-Institut für Astronomie der Universität Bonn and the Max-Planck-Institut für Radioastronomie in Bonn. [more]

Astronomy Walks in Effelsberg – how Sirius is coming to Chile

Scaled Extension of the Planetary Walk at the Effelsberg Radio Telescope to the Brighest Star in the Night Sky

September 14, 2018

The 100-m radio telescope of the Max Planck Institute for Radio Astronomy (MPIfR) is located in a valley near Bad Münstereifel-Effelsberg about 40 kilometers southwest of Bonn in the Eifel area. Three astronomical trails in the surroundings of the observatory, named “Planetary Walk”, “Milky Way Walk” and “Galaxy Walk” illustrate the complete cosmic distance scale from nearby planets to distant galaxies. The connection between two of them, the Planetary Walk and the Milky Way Walk, is established by the common target station “Sirius”.  In the scale of the Milky Way Walk, Sirius and our sun are neighbouring stations only 90 cm apart. In the scale of the Planetary Walk, the real distance of 8.6 light years between sun and Sirius amounts to 11,000 km, corresponding to the distance between two of MPIfR’s radio telescopes, the 100-m Effelsberg telescope in Germany and the 12-m APEX submillimeter telescope in Chile.  

The 100-m radio telescope seen from the courtyard of the visitors’ pavilion. The yellow ball marks the station “Sun” of the Effelsberg Planetary Walk. This walk includes 11 stations in total: the sun, 8 planets, dwarf planet Pluto and the nearby star Sirius as transatlantic extension. 
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The 100-m radio telescope seen from the courtyard of the visitors’ pavilion. The yellow ball marks the station “Sun” of[more]

Planet trails (in German: “Planetenwege”) are a nice way to illustrate cosmic distances and sizes within our solar system. They usually consist of nine or ten stations: the sun and eight planets, sometimes also including the dwarf planet Pluto. At the widely used scale of 1 : 1 billion the trail has a total length of almost 6 kilometers (distance between sun and Pluto). The sun scales to a diameter of 1.4 meters, and the Earth to 1.3 cm in a distance of 150 meters from the sun.

The Planetary Walk at the Effelsberg Radio Observatory is a bit smaller in size. Scaled 1 : 7.7 billion it covers the walking distance of about 800 meters from the parking area to the visitors’ pavilion where talks about radio astronomy and the telescope for groups of visitors are taking place. It starts with the dwarf planet Pluto at the parking lot and continues from there to the inner solar system – the rocky planets between Mars and Mercury and the sun itself can all be found at the courtyard of the visitors’ pavilion (Fig. 1).

Pluto (0 m) Visitors‘ Parking Area

Neptune (182 m) Road to Visitors‘ Pavilion

Uranus (389 m) Road to Visitors‘ Pavilion

Saturn (584 m) Road to Visitors‘ Pavilion

Jupiter (665 m) Road to Visitors‘ Pavilion

Mars (736 m) Road to Visitors‘ Pavilion

Earth (746 m) Court of Visitors‘ Pavilion

Venus (752 m) Court of Visitors‘ Pavilion

Mercury (758 m) Court of Visitors‘ Pavilion

Sun (766 m) Court of Visitors‘ Pavilion

Sirius (11,000 km) APEX Telescope, Atacama Desert, Chile

Table: Stations of the Planetary Walk at the Effelsberg Radio Telescope

Two additional walks, the Milky Way Walk and the Galaxy Walk, are extending the cosmic distance scale far beyond the solar system. The Milky Way Walk covers a total distance of 4 kilometers from the village Burgsahr in the nearby Sahrbach valley to a viewing spot immediately in front of the giant dish of the Effelsberg telescope. At a scale of 1 : 1017 (1 : 100 quadrillion) this corresponds to 40,000 light years through our galaxy. The Milky Way Walk includes a total of 18 stations from the outer regions along the sun to the Galactic centre at a distance of 25,000 light years from the sun.

The Galaxy Walk covers the truly large distances in the Universe. It has a total length of 2.6 km, starting in the forest behind the Effelsberg radio telescope and leading to a nearby hut (Martinshütte: the “hut at the edge of the Universe”). At a scale of 1 : 5 x 1022 (1 : 50 sextillions) it includes a total of 14 stations, the most distant one with a light travel time of 12.85 billion years. In other words: we observe light from that distant galaxy (named J1148+5251) coming from a time less than 1 billion years after the formation of the Universe.

In order to connect the three astronomy trails at Effelsberg there are two target stations included in two of the trails. The station “Andromeda Galaxy M 31” is contained in both, Milky Way Walk and Galaxy Walk. It is the closest large-scale spiral galaxy, a twin of our Milky Way at a distance of 2.5 million light years. For the Galaxy Walk that scales to 50 centimeters; Milky Way and Andromeda galaxy are the first two stations only 50 cm apart. At the scale of the Milky Way Walk, however, it corresponds to a distance of 250 kilometers.

The station “Andromeda Galaxy” is mounted at the “Haus der Astronomie” in Heidelberg, 250 km away from Effelsberg. This house is indeed shaped like a spiral galaxy, contains a 1 : 100 scale model of the Effelsberg telescope in its interior and the plaque “M 31” of the Effelsberg Milky Way Walk at the main entrance.

The connecting element between Planetary Walk and Milky Way Walk will be Sirius, the brightest star in the night sky. Sirius is a nearby star at a distance of only 8.6 light years from the sun. Both stations (Sun and Sirius) can be found on the Milky Way Walk: close to the village Binzenbach in the forest, the two plaques are just 90 centimeters apart.

For the Planetary Walk it is a different story: the distance of about 9 light years to Sirius scales to 11,000 kilometers! At the same scale, the dwarf planet Pluto is less than 800 meters away from the Sun. For the space probe Voyager 1, the most distant device built by mankind, it is less than 3 km in that scale, but even for the nearest star, Proxima Centauri, the distance is already more than 5000 km!

Coincidence by chance: the required value of 11,000 km for Sirius nicely meets the distance between two radio telescopes of the Max Planck Institute for Radio Astronomy, the 100-m radio telescope at Effelsberg and the APEX telescope in the Atacama desert in Chile which is  jointly run by the MPIfR, the European Southern Observatory ESO and the Swedish Onsala Observatory.

The station “Sirius” of the Planetary Walk is mounted directly at the APEX site on the Chajnantor plateau 5100 m above sea level in the Atacama desert (Fig. 2). Sirius is the brightest star in the night sky, and it is visible from both sites, Effelsberg in Germany as well as APEX in Chile.

Since there is no general access to the APEX telescope on Chajnantor, Sirius is also presented in the nearby village San Pedro de Atacama, 2500 m above sea level. The San Pedro office of Alain Maury’s San Pedro de Atacama Celestial Explorations (SPACE) on Caracoles 400-2 presents the plaque in three different languages (Spanish, English and German).

“It is great that Sirius enables us to close the last remaining gap between our astronomical walks at the Effelsberg telescope”, concludes Norbert Junkes from MPIfR who regularly uses the cosmic distance scale in his talks for visitor groups at the Effelsberg site. “From the planets to stars and star forming regions in our Galaxy and further on to other galaxies, almost to the edge of the Universe – our three walks cover the complete range.”

The Atacama Pathfinder Experiment (APEX) at the Chajnantor plateau in Northern Chile, 5100 m above sea level. The linear distance of 11,000 km between APEX and the Effelsberg 100-m radio telescope in Germany nicely corresponds to the distance of the nearby star Sirius in the scale of the Effelsberg Planetary Walk.
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The Atacama Pathfinder Experiment (APEX) at the Chajnantor plateau in Northern Chile, 5100 m above sea level. The linear[more]

Impact of a stellar intruder on our solar system

Computer models of a fly-by show amazing resemblance to outer solar system features

August 09, 2018

The solar system was formed from a protoplanetary disk consisting of gas and dust. Since the cumulative mass of all objects beyond Neptune is much smaller than expected and the bodies there have mostly inclined, eccentric orbits it is likely that some process restructured the outer solar system after its formation. Susanne Pfalzner from the Max Planck Institute for Radio Astronomy in Bonn, Germany and her colleagues present a study showing that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density in the outer part of the solar system and excite the bodies there onto eccentric, inclined orbits. Their numerical simulations show that many additional bodies at high inclinations still await discovery, perhaps including a sometimes postulated planet X.

The findings are published in the present issue of „The Astrophysical Journal“.

Artist’s concept of a solar system in the making with a protoplanetary disk surrounding a young star.
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Artist’s concept of a solar system in the making with a protoplanetary disk surrounding a young star.


A near catastrophy billions of years ago might have shaped the outer parts of the solar system, while leaving the inner regions basically untouched. Researchers from the Max Planck Institute for Radio Astronomy in Bonn and their collaborators found that a close fly-by of another star can explain many of the features observed in the outer solar system. „Our group has been looking for years at what fly-bys can do to other planetary systems never considering that we actually might live right in such a system”, says Susanne Pfalzner, the leading author of the project. “The beauty of this model lies in its simplicity.”

The basic scenario of the formation of the solar system has long been known: our Sun was born from a collapsing cloud of gas and dust. In the process a flat disk was formed where not only large planets grew but also smaller objects like the asteroids, dwarf planets etc.  Due to the flatness of the disk one would expect that the planets orbit in a single plane unless something dramatic happened afterwards. Looking at the solar system right to the orbit of Neptune everything seems fine: most planets move on fairly circular orbits and their orbital inclinations vary only slightly. However, beyond Neptune things become very messy. The biggest puzzle is the dwarf planet Sedna, which moves on an inclined, highly eccentric orbit and is so far outside, that it could not have been scattered by the planets there.

Just outside Neptune’s orbit another strange thing happens. The cumulative mass of all the objects dramatically drops by almost three orders of magnitude. This happens at approximately the same distance where everything becomes messy. It might be coincidental, but such conincidences are rare in Nature.

Susanne Pfalzner and her co-workers suggest that a star was approaching the Sun at an early stage, ‘stealing’ most of the outer material from the Sun’s protoplanetary disk and throwing what was left over into inclined and eccentric orbits. Performing thousands of computer simulations they checked what would happen when a star passes very close-by and perturbs the once larger disk. It turned out that the best fit for today’s outer solar systems comes from a perturbing star which had the same mass as the Sun or somewhat lighter (0.5-1 solar masses)  and flew past at approximately 3 times the distance of Neptune.

However, the most surprising thing for the researchers was that a fly-by does not only explain the strange orbits of the objects of the outer solar system, but also gives a natural explanation for several unexplained features of our Solar System, including the mass ratio between Neptune and Uranus, and the existence of two distinct populations of Kuiper Belt objects.

“It is important to keep exploring all the possible avenues for explaining the structure of the outer solar system. The data are increasing but still too sparse, so theories have a lot of wiggle room to develop”, says Pedro Lacerda from the Queen’s University in Belfast, a co-author of the paper. “There is a certain danger that one theory crystallises as truth, not because it explains the data better but because of other pressures. Our paper shows that a lot of what we currently know can be explained by something as simple as a stellar fly-by.”

The big question is the likelihood for such an event. Nowadays, fly-bys even hundreds of times more distant are luckily rare. However, stars like our Sun are typically born in large groups of stars which are much more densely packed.  Therefore, close fly-bys where significantly more common in the distant past. Performing another type of simulations, the team found that there was a 20%-30% chance of experiencing a fly-by over the first billion years of the Sun’s life.

This is no final proof that a stellar fly-by caused the messy features of the outer Solar System, but it can reproduce many observational facts and seems relatively realistic. So far it is the simplest explanation and if simplicity is a sign for validity this model is the best candidate so far.

„In summary, our close fly-by scenario offers a realistic alternative to present models suggested to explain the unexpected features of the outer solar system“, concludes Susanne Pfalzner. „It should be considered as an option for shaping the outer solar system. The strength of the fly-by hypothesis lies in the explanation of several outer solar system features by one single mechanism.“

Simulation of the stellar intruder scenario for a mass of 0.5 solar masses and a perihelion distance of 100 astronomical units or 15 billion kilometers for the perturbing star (three times the distance between Sun and Neptune). a) average positions of the particles after the fly-by, colors showing eccentricity of their orbits increasing from blue to green. b) particle positions before the fly-by with different eccentricity populations (colors) from the top row Grey regions: particles that became unbound due to the fly-by event.
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Simulation of the stellar intruder scenario for a mass of 0.5 solar masses and a perihelion distance of 100 astronomical units or 15 billion kilometers for the perturbing star (three times the distance between Sun and Neptune).[more]

26AlF – the first detection of a radioactive molecule in space

Tracing a rare molecular species in the remnant of an ancient stellar explosion

July 30, 2018

The first unambiguous observation of a radioactive molecule, 26AlF, was made in the ancient nova-like object CK Vul (or Nova Vul 1670), which – most likely – is a stellar-merger remnant. The eruption of the object was observed between 1670-1672 in Europe. The interest in this object has been recently rejuvenated by the discovery of molecular gas of a very peculiar isotopic composition in the remnant.An international research team led by Tomasz Kamiński from the Harvard-Smithsonian Center for Astrophysics and including Karl Menten from the Max Planck Institute for Radio Astronomy in Bonn, Germany, announces the findings, as Advanced Online Publication in Nature Astronomy (2018 July 30).
Color reproduction representing different components of the cool nebula surrounding the star CK Vul. Blue regions show emission of diazenylium (N2H+) and red regions represent methanol (CH3OH) emission; AlF emission is shown in cyan/green/yellow. The radioactive molecule of 26AlF was observed only in the very inner region of the complex. Part of the observed ionized molecules, like N2H+, may be produced by radioactive decays of 26Al. The warning sign at the lower left refers to the radioactive molecule 26AlF found in that nebula. Zoom Image

Color reproduction representing different components of the cool nebula surrounding the star CK Vul. Blue regions show[more]

The variable star CK Vulpeculae (CK Vul) is known as the location of a stellar outbreak, a nova, which was observed by European astronomers in the 17th century in the direction of the constellation “Vulpecula” (the little fox). Nova Vul 1670 was easily visible with the naked eye and varied in brightness significantly over the course of two years. It took a long time, until 2013, before astronomers, first using the Atacama Pathfinder Experiment telescope (APEX), could trace molecular gas of a very peculiar isotopic composition in the stellar remnant. Analysis of these very surprising findings indicated that a rare and spectacular stellar merger of two stars took place. The collision created a so-called red transient source or a red nova, a newly recognized class of eruptive stars.

The observation of the 26Al isotope provides direct insight into the merger process in CK Vul showing that even the deep and dense inner layers of the star can eventually be exposed in a stellar collision. More specifically, the observations constrain the nature of the binary system that merged more than 300 years ago: a low-mass binary that contained a red-giant-branch star of a mass of 0.8-2.5 solar masses.

This first direct observation of 26Al in a stellar-like object is also important in the broader context of the Galactic chemical evolution – this is the first time an active producer of the radioactive nuclide 26Al has been directly observationally identified. It has been known for decades that about two solar masses of 26Al is spread across the Galaxy. Although observable in gamma-ray emission, this radioactive cloud has unclear origin. With current estimates on the mass of 26Al in CK Vul and the Galactic merger rate, it seems rather unlikely that mergers are solely responsible for this Galactic radioactive material. However, the actual mass of 26Al in atomic form in CK Vul and other merger remnants may be much higher and the current merger rates can be very much underestimated, so this is not a closed issue and the role of mergers may be non-negligible.

In addition to putting into spotlight a new type of objects not considered before in the context of Galactic 26Al production, the discovery illustrates that modern millimeter-wave interferometers such as ALMA may be used to search for active 26Al producers at much better angular resolutions than gamma-ray observatories.

Another interesting aspect of the work is that the line positions were first calculated by molecular spectroscopists, who are co-authors of the study. Characterizing material containing 26Al in through direct measurements in a laboratory would be very challenging and expensive so calculations were the only practical option. The observed transitions match perfectly the predicted ones.

CK Vul remains an enigmatic source in the sky providing a playground for new astronomical detections.

Color reproduction of the nebula surrounding the star CK Vul (cf. Fig. 1), overlayed onto a night image of the ALMA antennas at 5100 m altitude on Chajnantor, Chile.   Zoom Image

Color reproduction of the nebula surrounding the star CK Vul (cf. Fig. 1), overlayed onto a night image of the ALMA[more]


The discovery involved the following telescopes/facilities: APEX, IRAM 30m, NOEMA, ALMA, and SMA. The most relevant observations were done with the transforming PdbI/NOEMA interferometer and with the ALMA array, including its newly commissioned band 5 receiver.

The research team comprises Tomasz Kamiński, Romuald Tylenda, Karl M. Menten, Amanda Karakas, Jan Martin Winters, Alexander A. Breier, Ka Tat Wong, Thomas F. Giesen, and Nimesh A. Patel.

Karl M. Menten, director at MPIfR and head of its Millimeter and Submillimeter Astronomy division, is co-author of the paper.

SOFIA and „Christmas comet“ Wirtanen

A bright „guest star“ is showing up in the night sky: comet 46P/Wirtanen. The airborne observatory SOFIA observed the comet in the nights from December 13 to 19 with the GREAT (German REceiver for Astronomy at Terahertz frequencies) instrument, built by MPIfR and Cologne University. In parallel, 46P/Wirtanen was observed with the APEX telescope in Chile (Clemens Plank, DLR Science Blog, December 2018, in German language). [more]