Beneficiary or preserver: Humpback whales in polar waters. - Foto: Alfred-Wegener-Institut.

According to Professor Dr Victor Smetacek of the Alfred Wegener Institute for Polar and Marine Research and Dr Stephen Nicol from the University of Tasmania in Hobart, Australia, the ability to predict changes in polar ecosystems within the context of global climate change requires a better understanding of the ecological role of whales and seals. In their contribution now published in the scientific journal Nature, the two researchers present the hypothesis that large marine mammals have a central and stabilising role in marine ecosystems and were once widely distributed across all oceans.

In analogy to the large fish stocks in African lakes being dependent on hippos, large mammals may also control their environment in the coldest oceans on earth. It is already clear that the notion of short food chains with few organisms represents an oversimplified view of polar ecosystems. in the productivity of the Arctic and Antarctic is comparable to temperate oceans. However, large differences exist between the Arctic and Antarctic with regard to nutrient availability and key species in the food chain. In the Antarctic, availability of iron is the primary growth-limiting factor in the system.

(2) Comments posted about this in the forum

The detection of a super massive black hole without a massive host galaxy is the surprising result from a large Hubble and VLT study of quasars. This is the first convincing discovery of such an object. One intriguing explanation is that the host galaxy may be made almost exclusively of dark matter.

No-host quasar compared with a normal quasar This figure shows two Hubble images of quasars from a sample of 20 relatively nearby quasars examined by a team of European astronomers two of the most powerful astronomical facilities available, the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT) at Cerro Paranal. The team confidently concludes that the quasar on the left, HE0450-2958 (in the centre, distance about 5 billion light-years) does not have a massive host galaxy. The quasar HE1239-2426 to the right (at a distance of 1.5 million light-years), has a normal host galaxy which displays large spiral arms. Although HE1239-2426 is much closer than HE0450-2958, the host galaxy of the latter would still be perfectly visible if it was as bright as the one of HE1239-2426. The lack of a prominent host galaxy around a very bright quasar (HE0450-2958) suggests a rare case of a collision between a seemingly normal spiral galaxy and an exotic object harbouring a very massive black hole. Also seen in the image to the left (above the quasar) is a strongly disturbed galaxy, showing all the signs of a recent collision. The VLT observations show it to be forming stars at a frantic rate. Below the quasar a foreground star is seen. The two images have been scaled to exhibit the same linear scale. The images were taken with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope. Image credit: NASA/ESA, ESO, Frédéric Courbin (Ecole Polytechnique Federale de Lausanne, Switzerland) & Pierre Magain (Universite de Liege, Belgium)

A team of European astronomers has used two of the most powerful astronomical facilities available, the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT) at Cerro Paranal, to confidently claim the discovery of a bright quasar without a massive host galaxy. Quasars are powerful and typically very distant source of prodigious amounts of radiation. They are commonly associated with galaxies containing an active central black hole.

The team conducted a detailed study of 20 relatively nearby quasars. For 19 of them, they found, as expected, that these super massive black holes are surrounded by a host galaxy. But when they studied the bright quasar HE0450-2958, located some 5 billion light-years away, they could not find evidence for a host galaxy. This, the astronomers suggest, may indicate a rare case of a collision between a seemingly normal spiral galaxy and an exotic object harbouring a very massive black hole.

With masses up to hundreds of millions that of the Sun, super massive black holes are commonly found in the centres of the most massive galaxies, including our own Milky Way. These black holes sometimes dramatically manifest themselves by devouring matter that they gravitationally swallow from their surroundings. The best fed of these shine as quasars (the name quasar is a contraction of quasi-stellar object, as they had initially been confused with stars).

The past decade of observations, largely with the Hubble telescope, has shown that quasars are normally associated with massive host galaxies. However, observing the host galaxy of a quasar is challenging work because the quasar completely outshines the host and masks the galaxy’s underlying structure.

(1) Comments posted about this in the forum

Two Olive Ridley turtles come ashore on the beaches of La Flor Wildlife Reserve in Nicaragua to nest. Photo courtesy of Terra Incognita Ecotours.

Nicaragua's majestic turtle migrations occur in waves referred to as "arribadas", or arrivals in Spanish. There is usually one "arribada" per month, but the exact date is influenced by a variety of factors, including the weather and moon. During each migration, several thousand turtles come ashore almost simultaneously and lay more than 100 ping-pong ball-sized eggs each. Remarkably, the turtles return to the exact same beach on which they were born, a phenomenon yet to be understood by scientists.

Both of Nicaragua's coasts are popular sites for nesting turtles. The country's less-developed Caribbean coast, specifically the Pearl Cays, is the nesting area of choice for thousands of rare Hawksbill, Green, Loggerhead, and Leatherback turtles. The warm water, inviting grass beds, and protective mangroves of these remote, white-sand beaches are also home to what is believed to be the world's largest remaining population of Green Sea Turtles. While visitors can only arrive via water or air, local charter operations such as La Costena, http://www.tacaregional.com/costena, and Atlantica Airlines provide flights to the region for less than $100.00 roundtrip.

(1) Comments posted about this in the forum