Se vienen tiempos turbulentos para las estrellas binarias

Otro astrobito… Esta vez sobre un artículo que publica un amigo mío, a punto de defender su tesis doctoral. Nuevos refinamientos de simulaciones hidrodinámicas han permitido “observar” grandes perturbaciones en la fase de envoltura común en estrellas binarias. Viene con vídeo y todo. ¡Espero que les guste!

Astrobites en español

• Título: “Hydrodynamic moving-mesh simulations of the common envelope phase in binary stellar systems” (arXiv version)
• Autores: Sebastian T. Ohlmann, Friedrich K. Röpke, Rüdiger Pakmor y Volker Springel
• Institución del primer autor: Heidelberger Institute für Theoretische Studien (Heidelberg, Alemania) & Institut für Theoretische Physik und Astrophysik (Würzburg, Alemania).
• Estado: Publicado en “The Astrophysical Journal Letters” el 1 de enero de 2016.

Las estrellas no son más que bolas de gas que queman hidrógeno en sus núcleos. La energía que se desprende de la fusión evita que la estrella colapse por su propia gravedad, hasta que el hidrógeno se acaba. Cuando el núcleo de la estrella se queda sin combustible, éste se contrae y las capas externas de la estrella se eyectan; la estrella se convierte en una gigante roja. En el caso de que la gigante roja tenga una compañera, la expulsión de las capas externas extrae energía y…

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Sobre el esquivo origen de las ráfagas rápidas de radio

Mi nuevo artículo en astrobitos, analizando el reciente resultado publicado en Nature en el que se encontraba por primera vez la galaxia huésped de una ráfaga rápida de radio. El esperado resultado, que causó revuelo en el campo, se desvaneció en tan sólo unos días cuando otros astrónomos trataron de revalidarlo y aportar nuevas observaciones. Cosas que pasan en la ciencia…

Astrobites en español

ARTÍCULO 1:

• Título: “The host galaxy of a fast radio burst”
• Autor: E. F. Keane et al.
• Institución del primer autor: Square Kilometer Array Organisation, Jodrell Bank Observatory, UK.
• Estado: Publicado en Nature el 25 de febrero de 2016

ARTÍCULO 2:

• Título: “Cosmological origin fro FRB 150418? Not so fast”
• Autor: P. K. G. Williams and E. Berger
• Institución de los autores: Harvard-Smithsonian Center for Astrophysics
• Estado: Enviado el 26 de febrero de 2016

Crédito de la imagen destacada: Fotografía de John Sarkissian, preparada por Adrian Pingstone (CSIRO, Parkes Observatory)

Las ráfagas rápidas de radio (FRBs, por sus siglas en inglés) son pulsos transitorios en radio que no duran más que unos pocos milisegundos. El primer evento de esta clase se descubrió en 2007, analizando datos de archivo tomados en 2001 con el radiotelescopio Parkes en Australia, retratado en la imagen destacada. A día de hoy se conocen un par de decenas de…

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Solar eclipse from Nijmegen

Europe was amazed one more time with a solar eclipse this morning. Luckily, a lot has changed since the times humanity feared the eclipse would take the sun away forever because of some divine punishment. Nobody thinks that eclipses are an act of god anymore. However, the excitement and the thrill that solar eclipses awake in us are still as intense as they used to be thousands of years ago.

It’s true; people are generally interested in astronomy. I often find myself answering a few questions about black holes or exoplanets right after being introduced as an astronomer. If the conversation turns into my research, I can have a hard time making the details understandable and explaining how society would benefit from my results. Astronomers do not have many chances to explain something that everybody can understand easily, and it is visible without the help of computer simulations. On the other hand, solar eclipses are spectacular, visually obvious and easy to explain. Solar eclipses are a perfect occasion to get people more interested in astronomy. They are one of the best chances that astronomers have to do outreach, which I believe is one of our duties as scientists. We could not do our research without the tax-payer money, and it is good that the general public learns more about how society benefits from our work.

Visitors at Radboud Observatory during the solar eclipse. Unfortunately, the fog prevented the observations.

I thought the Department of Astrophysics of Radboud University, where I work, should not miss this opportunity to host an activity for the general public. This is the reason I organised the public observation this morning. We had more than 200 visitors, despite the fog! I have really enjoyed it; people were very enthusiastic, asking their doubts about the eclipse. I would like to thank my colleagues, who were helping when the situation got very crowded. I don’t have pretty pictures of the eclipse as seen from Nijmegen. The weather was so bad that we could not see anything, so we could only guide the visitors to the telescopes. It is a pity that we could not show the eclipse, but, after all, we also depend on the weather for our research; that is why we go to locations like the Canary Islands, Hawaii or Chile. We also projected one of the live broadcasts from Iceland, were the eclipse was total. I remember especially the reaction of a 8-9 years old kid, who was even jumping when the totality exposed the solar corona and a few Baily’s beads. The drop in luminosity was noticeable, as you can see in the video that Dr Marco Langbroek shot from Leiden.

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During the public observation, I realised there is another reason to organise the observation of solar eclipses. We provided especial eclipse glasses, so direct observation of the sun is safe. To my surprise, some people did not believe that observing the eclipse with naked eye is harmful. I did not know the details of what happens to our eyes when we stare at the sun, but I have done my research. Maybe if I had used the term ‘solar retinopathy’, I would have been more convincing. Ultraviolet radiation causes light-sensitive cells in our retina to liberate chemical that damage our eyes [1]. The fact that the sun is less bright during the eclipse only increases the chances of permanent damage, as our pupil will not contract as usual. Of course, there are not systematic studies about how quickly this happens, but british doctors collected information during the solar eclipse in 1999, when around 70 people reported vision loss after staring at the sun for a few minutes [2, 3].

Eclipse glasses with the composition used to advertise the event.

Galileo Galilei is the well-known example of an astronomer loosing his vision during a solar eclipse. I have just learned that Galileo used to observe the sun with projection methods, and actually became blind due to a combination of cataracts and glaucoma [4]. I did not know when I spoke to the journalists this week. Scientists such as Thomas Harriot, John Greaves or Isaac Newton reported temporary vision loss after staring at the sun.

There are not total solar eclipses visible from Nijmegen this century. However, there are a few partial eclipses in the next years. I can only encourage people to enjoy these eclipses, but always in a safe manner!

Tanabata Matsuri tonight!

Vega and Altair are well known among star gazers, as they form together with Deneb the so-called Summer Triangle. The Summer Triangle leaves inside a portion of the Milky Way, and some of the most famous astronomical targets can be found in this patch of the sky, such as the “double-double star” or the Ring Nebula (M57), both in the constellation Lyra.

Summer Triangle.  Screenshot from Stellarium

Not to mention the historical importance of Vega itself in professional astronomy. Vega is the third brightest star in the sky, after Sirius and Arcturus, and its position was close to the northern celestial pole about 14000 years ago. It was also chosen as the reference star to define the brightness scale in different wavelengths. It was the first star different from the Sun to be photographed in 1872, and it has been extensively studied since the early beginnings of modern astronomy.

Photo of the Summer Triangle. By Sophie via her blog Belle Jeunesse.

But today I do not want to talk about professional astronomy. I have just learned about the Tanabata Matsuri, or Star Festival in Japanese. According to Chinese folklore, included later into the Japanese tradition, they were once two lovers called Orihime and Hikoboshi. Orihime was an immortal princess who dedicated her time to weave the finest of all garments while Hikoboshi was a mortal cow herder from a humble family. They fell deeply in love with each other in the very same instant they met. Orihime’s father found out about their love and became enraged. He condemned the lovers to be forever apart by sending each of them to a different shore to the Great Celestial River (the Milky Way). Orihime, personification of Vega, cried so much that the Universe was truly moved. On the seventh night of the seventh month thousands of magpies would be sent to build a bridge with their wings. Hikoboshi, represented by Altair, can cross then the Great Celestial River for only one night and the two lovers can be together. It is said that if it is cloudy, magpies cannot find their way to the Milky Way, and Orihime and Hikoboshi have to wait until next year, being eventual rain Orihime’s tears.

Orihime and Hikoboshi crossing the Great Celestial River over magpies’ wings. Image by Anhellica via Lilliacerise’s blog

Nowadays, people celebrate this tradition hanging their wishes, written in small pieces of paper, from bamboo.

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Vega y Altair son estrellas bien conocidas entre aquellos a los que les gusta observar el cielo nocturno, ya que forman uno de los lados del llamado Triángulo de Verano. Este forma geométrica, que ayuda a identificar las constelaciones en el cielo veraniego, encierra en su interior una porción de la Vía Láctea, y algunos de los objetos que los astrónomos aficionados observan a menudo se encuentran en esta parcela del cielo, tales como la Nebulosa del Anillo (M57) o la “doble-doble”, ambos en la constelación de la Lira.

Y eso sin mencionar la importancia histórica de Vega para la astronomía profesional. Vega es la tercera estrella más brillante en nuestro cielo, después de Sirio y Arturo, y su posición la situaba como estrella polar hace unos 14000 años. Fue elegida como estrella de referencia para definir los sistemas fotométricos en distintas longitudes de onda y fue la primera estrella fotografiada después del Sol en 1872. En definitiva, se ha estudiado muy intensamente desde los primeros días de la astronomía moderna.

Pero hoy no quería hablar de astronomía profesional, sin duda habrá tiempo para eso. Es que hoy acabo de enterarme de lo que es el Tanabata Matsuri, o Fiesta de las Estrellas en japonés. Según el folclore chino, que fue adoptado más tarde por la tradición japonesa, había una vez dos amantes llamados Orihime y Hikoboshi. Orihime era una princesa inmortal, que dedicaba su tiempo a tejer las más preciosas y finas prendas mientras que Hikoboshi era un humilde pastor de vacas. Un sólo instante bastó para que se enamoraran perdidamente desde el primer momento en que se vieron. El padre que Orihime, rey del cielo, no tardó en averiguar del romance que su hija mantenía con un mortal. Enfurecido, los condenó a estar separados para siempre, mandando a cada uno a una orilla diferente del Gran Río Celestial (la Vía Láctea). Orihime, personificación de la estrella Vega, lloró con tal desolación que el Universo se emocionó. Se dispuso que el séptimo día del séptimo mes una bandada de urracas volaría hasta las estrellas para construir un puente con sus alas. Así, Hikoboshi, representado por la estrella Altair, podría cruzar el Gran Río Celestial, y los amantes podrían estar juntos sólo por una noche. Se dice que cuando está nublado, las urracas no pueden ver las estrellas y Orihime e Hikoboshi tienen que esperar al año siguiente, siendo la lluvia las lágrimas de la princesa por no poder ver a su enamorado.

En la actualidad, la fiesta contiene elementos de la tradición de los “obons” y las personas escriben sus deseos en trozos pequeños de papel y los cuelgan de cañas de bambú.